Toxigenic cutaneous diphtheria in a returned traveller

Diphtheria is rarely reported in Australia. A case of cutaneous diphtheria was reported to the South Australian Department for Health and Ageing in April 2013 in an Australian-born 18-year-old female following travel in India. The case presented with a skin ulcer on her toe. Toxigenic Corynebacterium diphtheriae was isolated from a swab of the lesion. The case was treated with antibiotics. The public health response included infection control advice, assessing the case and household contacts for organism carriage and providing antimicrobial chemoprophylaxis to contacts. Although cutaneous diphtheria is not included as part of the Australian communicable disease surveillance case definition, this may be an oversight as international evidence demonstrates that it is a source of organism transmission and can potentially result in outbreaks among susceptible populations. This formed the rationale for the public health response to this particular case. The protocol for the public health management of diphtheria in South Australia has since been revised to include cutaneous lesions caused by the toxigenic strain of the organism as part of the surveillance case definition.

Ribosomal RNA-encoding DNA introgression across a narrow hybrid zone between two subspecies of grasshopper

A ribosomal RNA-encoding DNA (rDNA) cloned sequence, consisting of a 0.8-kilobase fragment from the 26S/nontranscribed spacer region, was used to identify diagnostic restriction enzyme fragments that distinguish the Moreton and Torresian subspecies of the grasshopper Caledia captiva. These restriction fragments were then used to study patterns of rDNA variation across a narrow geographical hybrid zone between the two subspecies. The pattern of rDNA variation that emerged after the analysis of over 250 individuals clearly demonstrates the asymmetrical introgression of the Moreton ribosomal RNA genes into the Torresian subspecies. This asymmetric movement of genetic material occurs even though there exists extreme postmating F(2) and backcross inviability between the two subspecies. From our data, as well as those of previous chromosomal and allozymic studies, we are able to support the occurrence of nonrandom processes such as biased gene conversion and/or natural selection. Because the rDNA loci in the Moreton and Torresian individuals are located in different regions on chromosomes 10 and 11, it should be possible to determine the relative contributions of conversion, natural selection, and these sorts of processes to the pattern of introgression of the Moreton rDNA into the Torresian subspecies.

Centromeres: moving chromosomes through space and time

Centromeres have played a pivotal role in the evolution of the eukaryote genome. Their indispensable involvement in chromosome segregation and the evolution of linkage groups throughout all eukaryotic lineages intuitively suggests conserved structure and function. Unexpectedly, recent molecular and biochemical analyses of centromeres have revealed highly divergent patterns in both DNA sequence and organization. Unlike the microtubules with which they interact, centromeres have undergone rapid diversification during evolution while retaining the same functional attributes. The most recent evidence indicates that centromeres may be species-specific entities composed of highly variable DNA families that interact with an array of non-histone proteins before attachment to the microtubules.

Hepatitis A outbreaks among illicit drug users and their contacts in Queensland, 1997

OBJECTIVE

To describe five outbreaks of hepatitis A virus (HAV) infection associated with illicit drug use during a statewide outbreak of HAV infection in Queensland.

DESIGN

Risk factor prevalence survey.

PATIENTS AND SETTING

All 875 cases of HAV infection notified to Public Health Units in Queensland in the 12 months to 30 November 1997.

MAIN OUTCOME MEASURE

Type and prevalence of illicit drug use.

RESULTS

Risk factor assessment was completed for 804 cases (91.9%). We identified five outbreaks of HAV infection linked to illicit drug use. These outbreaks accounted for 24.6% (215/875) of all notified cases and 39% (190/482) of notified cases in the 15-34 years age group. The main type of illicit drug use in four of the five outbreaks was injecting drug use (74%; 118/160), while in the other outbreak it was sharing of smoking implements for marijuana (38%; 21/55).

CONCLUSION

Illicit drug use may be an under-recognised risk factor for HAV infection, particularly in young people. Faecal-oral transmission through poor personal hygiene, including sharing of implements for smoking marijuana, is the most probable route of transmission in these drug-linked outbreaks. The role of contaminated drug and needle-sharing remains to be clarified.

Hemodynamic effects of gadodiamide injection and gadopentetate dimeglumine in anesthetized dogs

A nonionic (gadodiamide injection) and an ionic (gadopentetate dimeglumine) contrast medium were compared for their effect on hemodynamics in the anesthetized, open-chest dog. Both agents were administered i.v. over 15 s at dosages of 1.0 and 1.5 mmol/kg, in randomized order. Both contrast agents resulted in transient but statistically significant decreases in aortic pressure, left ventricular pressure, indices of left ventricular contractility and relaxation, and systemic and pulmonary vascular resistance, and increases in aortic blood flow. At each dosage investigated, the changes associated with the administration of gadodiamide injection were of significantly smaller magnitude than those seen after gadopentetate dimeglumine and returned to preadministration levels sooner. The results from this study confirm that gadodiamide injection produces less severe alterations in hemodynamics than gadopentetate dimeglumine.

Knowledge and use of oral rehydration therapy for childhood diarrhoea in Tumpat District

A community based study was conducted on the understanding and knowledge of childhood diarrhoea and use of oral rehydration therapy (ORT), in four selected villages in Tumpat District, Kelantan. The calculated annual incidence of diarrhoeal disease in children aged 0 to four years in all study villages was 1.38 episodes for each child. The main care-givers of children aged 0 to four years were interviewed and asked to demonstrate how to mix a standard ORS (oral rehydration solution) sachet if they had previously used ORT. Forty percent of care-givers had heard of the locally available ORT and 30% had actually used ORT. Of those who had heard of or used ORT, 10% had good knowledge of what it was and what it was used for, 51% had some knowledge and 39% had either no knowledge or inaccurate knowledge. Of care-givers who had previously used ORT only 20.5% demonstrated the correct volume of water to add to one sachet of ORT, but 82% would discard an unused solution within 24 hours. Significantly more literate women had used ORT than those not literate (p = 0.002). Mothers, particularly those literate, are the primary target group for ORT intervention strategies. Components of health education should include advice on what ORS is, what it is used for, and how to correctly mix a standard sachet.

The heterochromatin of grasshoppers from the Caledia captiva species complex. I. Sequence evolution and conservation in a highly repeated DNA family

The restriction enzyme TaqI digests 0.2% of the genomic DNA from the grasshopper Caledia captiva to a family of sequences 168 bp in length (length of consensus sequence). The sequence variation of this "Taq family" of repeat units was examined among four races from C. captiva to assay the pattern of evolution within this highly repeated DNA. The Taq-family repeats are located in C-banded heterochromatin on at least one member of each homologous pair of chromosomes; the locations range from centromeric to telomeric. Thirty-nine cloned repeats isolated from two population 1A individuals along with 11 clones from seven populations taken from three of the races demonstrated sequence variation at 72 positions. Pairwise comparisons of the cloned repeats, both within an individual and between different races, indicate that levels of intraspecific divergence, as measured by reproductive incompatibility, do not correlate with sequence divergence among the 168-bp repeats. A number of subsequences within the repeat remain unchanged among all 50 clones; the longest of these is 18 bp. That the same 18-bp subsequence is present in all clones examined is a finding that departs significantly (P less than 0.01) from what would be expected to occur at random. Two other cloned repeats, from a reproductively isolated race of C. captiva, have sequences that show 56% identity with this 18-bp conserved region. An analysis showed that the frequency of occurrence of an RsaI recognition site within the 168-bp repeat in the entire Taq family agreed with that found in the cloned sequences. These data, along with a partial sequence for the entire Taq family obtained by sequencing uncloned repeats, suggest that the consensus sequence from the cloned copies is representative of this highly repeated family and is not a biased sample resulting from the cloning procedure. The 18-bp conserved sequence is part of a 42-bp sequence that possesses dyad symmetry typical of protein-binding sites. We speculate that this may be significant in the evolution of the Taq family of sequences.

Pharmacokinetics and excretion of iohexol after lumbar myelography in man

Pharmacokinetics and excretion of iohexol, a new nonionic water-soluble contrast medium, were determined after lumbar myelography. Peak plasma concentrations were obtained 2 to 6 hours after injection and ranged from 29 to 177 microgram/ml. Terminal elimination half-life was 4.0 hours, and over 90% of the dose was recovered in the urine within 24 hours. In one patient with a large lumbar cauda equina tumor, absorption and excretion were delayed; but eventually 99% was recovered indicating a large capacity for reabsorption via the lumbar subarachnoid space. One mild headache of 5 minutes' duration was reported in a 73-year-old woman. No significant changes in vital signs, neurologic examinations, or serum chemistries were observed.

Iohexol: a new, nonionic agent in adult peripheral arteriography

The safety and efficacy of iohexol, a new nonionic contrast agent, were compared with a diatrizoate (Renografin-76) in a double-blind, parallel study of peripheral arteriography by femoral puncture in 60 patients. Extra-large field serial peripheral arteriography was used and a posterior tibial nerve block was applied to all patients in the study. Similar changes in blood chemistry were observed following the injection of iohexol and diatrizoate but these changes did not require corrective measures. Significantly more patients complained of a sensation of severe heat after receiving diatrizoate (38%) than after the injection of iohexol (10%) (p = 0.001). Four patients in the diatrizoate group experienced one or more adverse reactions, including mild urticaria. Only mild nausea was reported by a single patient in the iohexol group. Overall, 100% of the studies were diagnostic but more of the radiographs taken after the injection of iohexol were rated excellent than after the injection of diatrizoate.

A decidual cast following therapy with norethisterone

A case is presented of a decidual cast following progesterone therapy, an extraordinarily rare event.

Lumbar myelography with iohexol and metrizamide. A comparative multicenter prospective study

Diagnostic quality and adverse reactions associated with metrizamide and iohexol as contrast agents for lumbar myelography were compared in a prospective randomized double-blind study in 350 patients at seven centers. Both contrast media were administered in comparable volumes at a concentration of 180 mg I/ml. Overall quality of radiographic visualization was graded as "good" or "excellent" in 95% of 175 metrizamide studies and in 98% of 175 iohexol myelograms. Ninety-three patients examined with metrizamide (53%) and 130 patients studied with iohexol (74%) experienced no discomfort during or after myelography. The incidence of postmyelographic headache was 38% with metrizamide and 21% with iohexol. Nausea and vomiting were also more common with metrizamide. Five patients examined with metrizamide (3%) experienced transient confusion and disorientation after lumbar myelography. No such reactions were observed after iohexol myelography.

Iohexol cerebral angiography. Multicenter clinical trial

Ionic contrast media currently used in cerebral angiography frequently cause discomfort due to hyperosmolality. This double-blind, multicenter trial compared two ionic media, meglumine iothalamate and meglumine-Na diatrizoate, with the new nonionic agent, iohexol, in 277 patients undergoing cerebral angiography. Vital signs, cardiovascular changes, and neurologic status were evaluated before, during, and after injection. Patients were observed for adverse reactions for up to 24 hours following studies. Patient discomfort and image quality were evaluated. Visualization was good or excellent with all media studied. No significant physiological differences were observed between the ionic and iohexol groups, but fewer iohexol patients experienced large increases (greater than 20 mmHg) in systolic blood pressure. Iohexol patients experienced significantly less discomfort; ionic patients reported severe discomfort 21/2 times more often. This finding was attributed to iohexol's low osmolality. Iohexol may be indicated particularly for use in selective angiograms where discomfort is a factor and for patients suspected of having blood-brain barrier disruption.

Toxicology of iohexol

This review summarizes the biological profile of the nonionic contrast medium, iohexol, with particular emphasis on neurovascular and myelographic applications. Iohexol was compared with conventional ionic media and with newer nonionic agents in a variety of animal models. Studies of systemic toxicity (teratogenicity, mutagenicity, and embryotoxicity effects) and cerebrovascular effects (epileptogenicity and arachnoiditis potential) are reported. Results indicate that iohexol has a lower toxicity than ionic and other nonionic contrast media.

Summary of U.S. and European intravascular experience with iohexol based on the clinical trial program

The nonionic contrast medium, iohexol, was released by Nyegaard, Oslo, in 1980 for clinical testing. Results of a three-phase clinical trial program carried out in Europe and the U.S. through December 1983 are summarized. Evaluation of phase I studies of human tolerance and excretion--and phase II studies of effects on pharmacologic and physiologic parameters--indicated that iohexol was well tolerated and effective. Phase III consisted mainly of controlled parallel and crossover studies comparing iohexol with conventional ionic media and with other nonionic agents in a variety of radiographic studies. Image quality was as good or better with iohexol than with ionic media. Iohexol was tolerated significantly better than ionic agents. Patients consistently reported fewer and less intense pain and heat sensations. Iohexol had less effect on blood pressure, blood flow, heart rate, and electrophysiologic parameters, and caused fewer adverse reactions than ionic media for all types of reactions observed.

Iohexol vs. metrizamide: study of efficacy and morbidity in cervical myelography

A double-blind study was conducted in 60 patients undergoing either cervical or more complete myelography via C1-C2 puncture. Patients received either iohexol or metrizamide at a 300 mg l/ml concentration. The contrast media were equally efficacious in the production of high-quality radiographs and CT scans. However, the incidence of adverse reactions differed markedly. Of patients receiving metrizamide, 68% had some type of adverse reaction, whereas only 26% receiving iohexol had symptoms. The incidence of headache (metrizamide, 34%; iohexol, 26%) was not statistically different, but the quality of the headache differed: half of the metrizamide headaches were moderate or severe, whereas all iohexol headaches were mild. Nausea (31%) and vomiting (28%) were common with metrizamide but unusual (3% nausea) with iohexol. Of the metrizamide patients, 21% had overt psychologic changes that did not occur in the iohexol group.

Iohexol: summary of North American and European clinical trials in adult lumbar, thoracic, and cervical myelography with a new nonionic contrast medium

Iohexol, a new water-soluble nonionic contrast medium, was evaluated in clinical trials in Europe and North America for lumbar, thoracic, and cervical myelography using direct C1-2 or lumbar puncture. Iohexol was administered at 180, 240, or 300 mg I/ml to 677 adult patients for visualization of the lumbar subarachnoid space, and to 368 adult patients for evaluation of the cervical area. Compared with metrizamide, use of iohexol resulted in equivalent opacification but significantly reduced patient morbidity (headache, nausea, vomiting, dizziness). No epileptogenic activity was recorded in over 370 patients receiving iohexol. No mental or psycho-organic syndrome manifestations were observed in any of the 1,045 patients receiving iohexol. Adverse reactions occurring after iohexol injection were not related to the concentration or site used or to total dose administered. Iohexol has, thus far, proven superior to metrizamide for myelography.

Iohexol for cervical myelography via C1-C2 puncture: study of efficacy and adverse reactions

Cervical myelography with iohexol via C1-C2 puncture was performed in 30 patients in two medical centers using a concentration of 240 mg l/ml. The study demonstrated iohexol to be a safe contrast medium without significant changes in neurologic and physical examination, vital signs, electrocardiogram, or hematologic or blood chemistry parameters. Fifteen patients had electroencephalograms (EEGs); two were abnormal. In one patient the baseline EEG demonstrated nonspecific slow waves in the temporal regions bilaterally that remained unchanged after myelography. In the second patient, transient changes in the left hemisphere during either hyperventilation or photic stimulation on postmyelographic EEG had not been present on the baseline recording. The relation of these changes to the drug remains unclear. Iohexol was found to be an efficacious myelographic contrast agent, with good to excellent myelograms in 93% of cases. Headache occurred in 13% and nausea in 3%.

Cranial and spinal cerebrospinal fluid absorption and the clearance of water-soluble myelographic contrast media. A review

Following myelography, water-soluble contrast media are cleared from the subarachnoid space with the cerebrospinal fluid via the cranial and spinal absorption pathways. These cerebrospinal fluid absorption pathways are reviewed. The effects of removal of excessive quantities of cerebrospinal fluid, increased numbers of cells in the cerebrospinal fluid, and dehydration are discussed.

Lumbar myelography with iohexol and metrizamide: a comparative multicenter prospective study

Diagnostic quality of radiographs and adverse reactions associated with the use of metrizamide and iohexol as contrast agents in lumbar myelography were compared in a prospective randomized double blind study in 350 patients at seven centers. The contrast media were administered in comparable volumes at a concentration of 180 mg I per ml. Overall quality of radiographic visualization was graded good or excellent in 95% of 175 metrizamide studies and in 98% of 175 iohexol studies. Ninety-three patients examined using metrizamide (53%) and 130 patients examined using iohexol (74%) experienced no discomfort during or after myelography. Postmyelographic headache was associated with 38% of metrizamide examinations and 21% of iohexol examinations. Nausea and vomiting were also more common with metrizamide. Five patients examined using metrizamide (3%) experienced transient confusion and disorientation following lumbar myelography. No such reactions were observed following iohexol myelography.

Increased chromosomal mutation rate after hybridization between two subspecies of grasshoppers

Hybridization between two chromosomally distinct subspecies of the grasshopper Caledia captiva results in a high incidence of novel chromosomal rearrangements among the backcross progeny. Rearrangements are restricted to those chromosomes derived from the F1 hybrid parent. Chromosomal involvement is nonrandom with the same rearrangement occurring repeatedly in different backcrosses. A single individual can also generate an array of different rearrangements among its offspring. Several of the rearrangements have also been found in natural populations. The nonrandom and recurrent nature of these chromosomal mutations at high frequencies provides a plausible explanation for the establishment and fixation of chromosomal rearrangements in natural populations.

Metrizamide, iothalamate, and metrizoate: effects of internal carotid arterial injections on the blood-brain barrier of the rabbit

Experiments were conducted on anesthetized rabbits to determine the effect of internal carotid artery injection of various contrast media on permeability changes in the blood-brain barrier. Changes in respiratory pattern, neuromuscular effects, and trypan blue extravasation were recorded after 3-ml injections of ionic and nonionic contrast media. Metrizamide and iothalamate meglumine were compared at iodine doses of 300, 400, and 500 mg I/ml. Metrizoate at 280 and 440 mg I/ml and diatrizoate meglumine at 385 mg I/ml were also included for comparison. The results demonstrated that metrizamide at all three iodine concentrations used caused minimal disruption of the blood-brain barrier, the effect being no greater, statistically, than saline controls. Iothalamate was benign at the lowest iodine concentration, but caused significant barrier breakdown at the two higher concentrations. These results suggest that alterations in blood-brain barrier permeability following angiography are mediated by both hyperosmolality of the contrast medium and the chemotoxicity of the contrast molecule.

Assessment of healing of long-bone fractures by intraosseous venography

Intraosseous venography with compression of the soft tissue was performed following fracture of the radius in 13 dogs to assess the repair process. Two angiographic criteria were analyzed: (a) intraosseous venous crossing of the fracture ("medullary crossing") and (b) capillary blush of the proximal osseous fragment ("proximal blush"). The bone strength of the fractured and intact radii was compared. Venograms obtained immediately after fracture showed contrast material reaching but not crossing the fracture line, indicating that the entire intramedullary venous network had been disrupted. When Parafilm was interposed between the bone fragments to prevent healing, proximal blush was seen at 4 weeks and medullary crossing at 6-7 weeks; bone strength was 13-14% of normal. With no barrier, proximal blush appeared at 5 weeks and medullary crossing at 10-11 weeks; bone strength was 30-40% of normal. The authors conclude that medullary crossing can be seen in the presence of decreased bone strength if the healing process is uneven across the fracture line, as occurred with Parafilm. If the animal model reproduces the clinical situation, this finding challenges the predictive value of intraosseous venography.

Role of peripheral vasodilation in the hypotensive response to left ventriculography in anesthetized dogs

Hypotension after left ventriculography (LVG) is believed to result from direct myocardial toxicity, peripheral vasodilation, or a combination of both. The contribution of each has not been established. Thus, LVG was performed in anesthetized dogs under conditions in which peripheral vascular reactivity (PVR) was altered pathophysiologically (aortic coarctation) or pharmacologically (acetylcholine infusion). Ventricular pressure (LVP), its first derivative (dP/dt), aortic pressure (AoP), and carotid and femoral flows were monitored. When PVR was normal, LVG was associated with significant hemodynamic changes which reached a maximum 25-35 seconds after injection. Left ventricular and aortic diastolic pressures were decreased by 22 and 48%, whereas carotid and femoral systolic flows were increased by 41 and 59%. During acetylcholine infusion, LVG did not cause systolic hypotension and peripheral flows were maintained strikingly constant. Similarly, LVG also was associated with insignificant changes in systolic pressures and carotid flow in the presence of aortic coarctation. These results demonstrate that the hypotension attendant with LVG is directly related to the augmentation in peripheral flow, suggesting that the response is mediated almost exclusively by peripheral vasodilation.

A comparison of chromosomal and allozymal variation across a narrow hybrid zone in the grasshopper Caledia captiva

A hydrid zone between the Moreton and Torresian taxa of the grasshopper Caledia captiva in S.E. Queensland has been characterised in terms of allozyme and chromosome variation within the same individuals.--On chromosomal criteria (pericentric rearrangements), the zone is asymmetrical with evidence of high levels of introgression of Torresian chromosomes into the Moreton taxon. This is apparent from the analysis of two independent transects across the hydrid zone. Major changes in chromosomal frequency occur over distances of less than 0.5 km. and the level of introgression differs between the two transects, with much higher levels in the northern Moreton populations, characterised by an acrocentric X-chromosome, when compared with the southern metacentric-X Moreton populations. Chromosome analysis of samples taken from the same transect over two years has revealed no major changes in the structure of the zone. Moreover, a Moreton population located only 0.5 km. from the null point was found to be stable over 6 generations with evidence for a new balanced genome having originated following the differential incorportation of Torresian chromosomes.--Contrary to the chromosomal situation, the same hybrid zone was found to be symmetrical with respect to allozyme variation with evidence of movement of diagnostic alleles in both directions across the zone. The alleles are independent and not tightly linked to any of the pericentric rearrangements. Thus these 5 alleles are acting as markers of the background genome and reveal the relatively free movement of genes which are located outside the pericentric rearrangements.--It is proposed that the hybrid zone in Caledia captiva is unstable and is moving slowly in a westerly direction into the Torresian territory. This is due to the ability of the Moreton taxon to incorporate more readily into its genome those Torresian chromosomes or chromosome segments which increase the fitness of the Moreton taxon. On chromosomal criteria, the Torresian taxon does not share the same capacity.--It is suggested that, so long as the two taxa retain their ability to hybridise with subsequent asymmetrical introgression, the zone will continue to move westwards and eventually lead to the selective incorporation of the Torresian genome into the Moreton taxon. This will result in a polymorphic situation with clinal variation in chromosomal frequencies. The structure of the zone is dependent upon a fine balance between genomic reorganisation in recombinant genotypes and the relative dispersal capacities of the two hydridising taxa.

A proposed mechanism for transient increases in arterial pressure and flow during angiographic injections

In a series of animal experiments, we have confirmed the observation that arterial pressure and flow increase distal to the injection site during power injections through non-obstructing catheters. Our data suggest that the phenomenon is secondary to the transient production of turbulence. Thus, for a given injection rate, catheters with smaller end holes create more fluid velocity, which increases the Reynolds number and causes augmentation of downstream pressure and flow. The addition of side holes decreases the fluid velocity of the injectate and minimizes the hemodynamic effects. The discussion deals with factors contributing to the generation of local turbulence, the magnitude of pressure and flow changes caused by the injections, and the clinical implications of these artifacts.

Distinguishing ischemic from fibrotic myocardium during ventriculograpy by means of physiological potentiation

Physiological potentiation during ventriculography is more helpful than the routine ventriculogram in predicting postoperative ventricular function. The authors describe a control device which allows the operator to flexibly program a pacing stimulus, thus making it possible to obtain both a resting beat and an optimum potentiated beat during a single ventriculographic study.

Accuracy of estimates of contrast media concentration

An animal model was used to prepare 18 experimental roentgenograms with differing dilutions of Conray 400 in each renal pelvis. Fifty radiologists were asked to estimate the iodine concentrations after they had been shown examples with known iodine concentrations. It was found there was a great deal of variation in the ability of individual subjects to accurately estimate the iodine concentration present. When the urinary iodine was less than 25 mg/ml, contrast estimations became grossly unreliable. At higher concentrations, the average performance of the sixty subjects was fairly clos to observed densotimetric readings. This study demonstrates that the ability to estimate iodine concentration is similar to other perceptive abilities in demonstrating both thereshold sensitivity and a near normal distribution among observes of the ability to judge perceptable differences in contrast media density.

Regional distribution of coronary blood flow during left ventriculography in anesthetized dogs

Changes in total and regional left coronary blood flow in response to ventriculography were studied using electromagnetic and microsphere techniques. Correlation of coronary flows by these methods showed excellent agreement (r = 0.947). Ventriculography produced a characteristic triphasic response in total flow and in endocardial/epicardial perfusion ratios. Changes in coronary flow can be explained as a result of hypotension and vasodilatation.

Comparative chiasma analysis using a computerised optical digitiser

A new computerised technique has been devised for measuring the distribution of chiasmata along diplotene bivalents. The method involves the introduction into the field of view of the microscope, of a fine light spot which can be accurately manipulated along the chromosomes of each bivalent. The data recorded include (a) the positions of the chiasmata along the bivalent in terms of their relative distances from the centromere and (b) the individual bivalent and cellular chiasma frequencies. -- The method has been applied to the analysis of chiasma distribution patterns in the two known species of the genus Caledia, C. species nova 1 and C. captiva and in two chromosomal races of the latter. Statistical tests indicate that within bivalents at least 40% of the comparative distribution patterns of chiasmata between races and species are significantly different. Similar comparisons between populations within races reveal only 18% significant differences. -- The observed distribution patterns of chiasmata in this genus suggest that chiasma formation is sequential from centromere to telomere. -- The variation in the frequency and distribution of chiasmata between races and species suggests that the interference distances between successive chiasmata are, at least partially, independent of chiasma frequency and position. -- The interracial and interspecific differences in chromosome structure are correlated with changes in chiasma pattern.

Population cytogenetics of the genus Caledia (Orthoptera: Acridinae). II. Variation in the pattern of C-banding

The distribution of constitutive heterochromatin has been investigated in four chromosomal races of the grasshopper Caledia captiva (2n=23 male/24 female) by the C-banding technique. Each of the four races was found to have a distinctive banding pattern which is associated with the inter-racial differences in chromosomal rearrangements. The "Ancestral" race has a telocentric chromosome complements with large procentric C-bands which are structurally double on six pairs of chromosomes. The centromeres are unstained. The "General Purpose" race has a C-banding pattern very similar to that seen in other Acridine grasshoppers with the majority of its chromosomes showing a centromeric localisation of the bands. The two southern races, which show a complex polymorphism for presumed pericentric inversions on all twelve chromosomes, also show an unusually high level of interstitial and terminal C-bands. The different locations and numbers of these bands allow unambiguous identification of all the chromosome pairs within the complement. In two cases, there is good evidence to indicate that a C-band redistribution between acrocentric and metacentric chromosomes has occurred by pericentric inversion. Furthermore, C-band variation on the long arm of the metacentric X-chromosome indicates the presence of a large paracentric inversion. This double inversion system has involved over 95% of the X-chromosome. The interstitial and terminal C-bands probably have not resulted from heterochromatin movement within the complement but, more likely, have arisen by saltatory duplication of pre-existing sequences on the chromosome. A new nomenclature system for banded chromosomes is proposed which allows most kinds of chromosomal restructuring and rearrangement to be adequately enumerated.

Population cytogenetics of the genus Caledia (Orthoptera: Acridinae). I. Inter- and intraspecific karyotype diversity

The genus Caledia acontains two species. C. species nova 1 is restricted to the Oriomo Plateau of S. W. Papua and has a complement of twelve telocentric chromosomes. The second species C. captiva has a much wider distribution pattern--from S.W. Papua in the North, down the entire Eastern seaboard of Australia to Southern Victoria. It is also found in the Northern Territory. Although the chromosome number is the same as C. species nova 1, four major and distinct chromosomal races can be distinguished in C. captiva.--The basic "ancestral" race is found in Tropical North Queensland at the base of the Cape York Peninsula. All twelve chromosomes are telocentric and the karyotypic organization is similar to that found in C. species nova 1 and in other Acridines. A second, "general purpose" karyotypic race has a wide distribution between S. W. Papua, Arnhem Land and the East Australian coast as far South as Brisbane. It is considered a derivative form of the "ancestral" type and is fixed for small pericentric inversions on seven pairs of chromosomes. In the South-Eastern Queensland region there exists a further race which carries large pericentric inversions on all the autosomes and the X chromosome. The situation here is confounded since the basic chromosomes can be represented as either acro- or telocentrics. Various levels of polymorphism for the inversions exist between different chromosomes in different populations indicating considerable differentiation within this zone. This race is almost completely surrounded by the "general purpose" karyotype where the races are contiguous in certain parts of the range.--The South-Eastern corner of Australia is characterised by a chromosome race quite different from those found further North. Here a complex pericentric inversion system exists involving a series of seven small inversions and larger inversions on chromosomes 1, 2, 4 and 10. Chromosomes 2 and 4, in particular, are highly polymorphic.--The presence and persistence of these 4 chromosomal races can be accounted for in terms of the known climatic changes which have occured in this region in the recent past.

The effect of angiotensin-II during ventriculography in dogs with normal coronary arteries

Left ventriculography was performed with and without angiotensin-II in dogs with normal coronary arteries. Concomitant administration of angiotensin significantly attenuated the myocardial depression associated with ventriculography. The beneficial effect of angiotensin may be due to its ability to maintain aortic diastolic pressure and thus flush the contrast material from the myocardium more rapidly, at least in animals without imposed coronary stenosis.

Selection for supernumerary Y-chromosomes in Dermestes maculatus (Coleoptera: Dermestidae)

A selection programme, carried out over 4 generations in an Indian strain of Dermestes maculatus carrying supernumerary y-chromosomes, led to an increase in the number of y-chromosomes up to a maximum of 4. It also resulted in a progressive increase in the frequency of Xyyy males from 4% in the unselected base stock to 54% and 53% in the S3 and S4 generations respectively.These selective increases were accompanied by a decreased stability of the sex multiple due to the inability of the X-organised sex nucleolus to efficiently accommodate more than two y-chromosomes.In S3 and S4, 21 out of 92 matings gave significant deviations from the expected 1:1 sex ratio and led to the production of an excess of males. This excess is thought to have resulted from the formation of Xyn sperm which failed to realise viable products.It is suggested that these findings have two important implications for the evolution of sex chromosome systems in beetles. First, they explain the absence of Xyn multiple mechanisms in natural populations and, second, they argue for a genetical, as opposed to a purely mechanical, function for the y-chromosome in the males of Xyp species.

An Improved Method for the Study of Nutritional Anemia in the White Rat

Experiments in our laboratory have demonstrated that white rats fed only fresh whole milk secured enough minerals from their cages to prevent anemia. Animals consuming large amounts of milk became anemic more quickly than those limited to small amounts. Access to feces delayed somewhat the onset of anemia. These results probably explain some of the conflicting data reported in the literature and also raise a question regarding the correctness of conclusions drawn from experiments in which recognition was not given the factors shown in this study to be important.