The mechanical properties of bone cements

The mechanical properties of a number of commercially available bone cements have been investigated. Tests were carried out on specimens in compression, in bending and in tension. Using the compression test as a standard, the effects of the following variables were studied: the addition of antibiotics, strain rate, environmental temperature, and age. It was concluded that age, temperature and rate of straining have a marked effect on the strength of the cement, while the addition of small quantities of antibiotics only marginally weakens the cement.

In vitro aging of frozen bull semen

The change in fertility of bull semen with time in storage at -196 C was examined in data on inseminations by the Michigan Animal Breeders Cooperative over 5 yr. Intervals from collection to use were grouped by 10 days for the 1st yr, 30 days for the 2nd yr, 180 days for the 3rd yr, and a single class for semen stored 4 or 5 yr. There were 97,586 first inseminations from bulls with 10 or more ejaculates and from ejaculates with four or more classes. Nonreturn rates for 50-, 60-, 90-, and 180-day intervals post-breeding were calculated. Heterogeneity of quadratic regressions of nonreturn rates on semen age was unimportant. Both regression and least squares analyses were used. Nonreturn rates increased to about 115 days of storage and remained there through the 4 and 5 yr age group. The lowest and highest nonreturn rates for a return interval differed by approximately 4%. Maximum differences in nonreturn rates for different intervals were at the lowest nonreturn rates.

Selection effects on a linked neutral locus

Selection changes the frequency of alleles at a linked locus as well as at those under selection if the population is not in linkage equilibrium. The magnitude of this frequency change depends on the tightness of the linkage, the selection intensity, and the deviation from linkage equilibrium. Allowing a population to mate randomly without selection brings the population closer to linkage equilibrium. This decreases the effect of selection on allelic frequencies at a linked neutral locus. However, if linkage is very tight it can take many generations to make a large difference in the effect of the linked locus. The loss due to undesirable changes in allelic frequencies at linked loci when the population is not in linkage equilibrium must be weighed against the time and effort saved by beginning intense selection for the primary trait in an early generation. Effects of selection intensity, linkage intensity, and delayed selection on changes in allelic frequency at a neutral linked locus are demonstrated.

Thermal aspects of self-curing polymethylmethacrylate

Bone necrosis adjacent to self-curing polymethylmethacrylate is a matter of accepted fact. Among the possible causes are mechanical and vascular damage from the preparation of the bone cavity, chemical damage from the monomer and free radicals in the cement dough, and thermal damage from the heat of polymerisation, occurring in this order. Consideration of the tissue reaction to this material, theoretical calculation of the heat output from polymerising acrylic and interface temperature profiles, experimental observations of interface temperatures and maximal temperatures at polymerisation, together with clinical observations, all lead to the view that the bone necrosis is not a consequence of thermal damage, which is unlikely to be a cuase of failure of prosthetic fixation. Temperatures recorded from within polymerising acrylic masses are related primarily to the amount of monomer polymerising and are of no clinical significance in the fixation of prostheses. Interface temperatures are related primarily to the surface area of the interface and the thermal characteristics of the cooler material.

Preweaning growth of inbred, F 1 hybrid, and random-bred mice as a measure of mother's lactation

A cross-fostering experiment was performed in which inbred and random-bred mothers suckled three groups of young: inbred (the SWR strain), F1hybrid (SWR × C3H), and random-bred (originally synthesized from SWR, C3H, CBA and C57BL). Two inbred mothers and one random-bred mother were placed in each of 43 cross-fostering sets, and each mother suckled two of her own young and two from each of the other two mothers. Body weights of young were recorded individually at birth and at 12 days.In 12-day weight and gain from birth to 12 days, differences among the three groups of young and differences between inbred and random-bred mothers were significant (P < 0.01). Although the ratios of the between-dam to within-dam mean squares in log scale varied among nine mother-young subgroups, the differences between any pair of these ratios were statistically insignificant. It was therefore concluded that in detecting lactation differences among mothers the value of a given type of young was not different between inbred and random-bred mothers and that as a means of detecting lactation differences among random-bred mothers, inbred and F1hybrid young did not appear to offer any substantial advantage over random-bred young.