The epidemics of Sendai virus characterized by snuffles occurred repeatedly at intervals of 8 to 10 months in a rat breeding colony of approximately 500 animals.
Outbreaks spread out over the whole colony rapidly and persisted for 2 to 3 weeks, but sometimes a limited incidence of snuff les was observed at 2 to 6 weeks after the termination of epidemics. During each epidemic, the delayed growth of youngs and the decreased weaning rate were observed. At autopsy of rats having shown snuffles the red consolidation was found in the lungs, from which a hemagglutinating virus was isolated and identified as Sendai virus by HI test. In animals exposed to the infection, there was a significant elevation of Sendai virus HI antibody titer coincidentally with each outbreak and the antibody was detectable even one year later. The rats born after the termination of an epidemic, however, had no antibody until the next outbreak. Mycoplasma was isolated from the lungs in one epidemy during a 2 year period. These findings might represent an epidemiological pattern of Sendai virus in a rat breeding colony where susceptible animals attain periodically a population large enough to provoke a new outbreak.

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A mutant was found in the course of mating experiments between S III, which was characterized by suckling death, and C57BL/6JNga. The symptoms of this are creeping or rolling in a poor motor control of hind limbs, and sometimes, mutant a stiff of hind legs and tail, and recognized from 10 to 14 days after birth. In genetical studies, the mutant is considered to be controlled by a single autosomal recessive gene. The symbol of this gene is proposed as “rol” based on the rolling mouse Nagoya. The rolling mouse is conjèctured to have a cerebellum abnormarity and may be used as a model animal in biomedical fields. The rolling female is fertile but low in ability of breeding and nursing‘ compared with a normal stanard female, and the male is almost infertile because of a bad coition. Rolling mice born in the inbreeding line are weak, but segregated rolling mice from cross breeding are stable in viability compared with one in the inbreeding line. Based on these conditions, the breeding system of this mutant strain was planned to maintain the mutant gene and also to produce more rolling mice. In this case, animals for maintenance, for production and for experiment must be considered to distinct clearly. So the cross-intercross system with rotational crossing using the rolling female is proposed for maintenance of the“rol”gene, or the nucleus of this mutant strain. In this mating system, the heterosis is effective in prevention of inbreeding depretion. It is advisable to make congenic strains or coisogenic strains for production, and to produce rolling mice for experiment from these strains.

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Based upon the findings of aquired resistance after natural infection, effective vaccination with killed organisms and the resistance due to maternal antibodies, as repo rted previously, two attempts were made at eradicatingB. bronchisepticafrom guinea pig breeding colonies. First, it was intended to remove all animals still excreting the organisms as well as uninfected animals from the colony and to establish anew colony. After such depopulation was continued for 4 months, the detection rate of the organisms was found to lower to 11 per cent from 78 per cent at the begin fling of the experiment. Finally, in 6 months, 73 breeders carrying no organisms were selected from a stock colony consisting of 128 guinea pigs for establishing a new colony, which was proved to be free of the organisms by repeated checking for further 5 months. Another attempt was made to establish a free colony by vaccination with killed organisms. In a colony consisting of 108 breeders and their offspring and showing 71.3 per cent at the highest detection rate of the organisms, all breeders were injected with merthiolate-killed vaccine, without interruption of breeding. Beginning 4 months later, breeders shedding the organisms were destroyed, and the eradication was successfully achieved also in this colony.

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Mice from a breeder corony producing 6, 000 mice per week were examined for complement fixing antibody against mouse hepatitis virus (MHV) by anamnestic response. Just before the first antibody detection in retired breeder mice, a decrease in weaning rate was observed, but it recovered with increase in antibody positivity in retired breeders. Thereafter, the antibody was detected at monthly monitering in them for over 3 years and the positive rate and titer showed a cyclic variation of 7 or 8 months. Mice weaned at a time when the positivity of retired breeder mice was comparatively high had no detectable antibody at 3 of 4 weeks of age, but 21 to 26% of those of age 5 or 6 weeks had the antibody. Even when such mice as mentioned above were isolated from the infected colony into a MHV-free environment at 3 or 4 weeks of age, the antibody also appeared later in their sera. However, when pregnant mice having been exposed naturally to MHV infection were isolated intoa MHV-free environment before belivery, their progenies were found to have no detectable antibody at 6 to 10 weeks of age, while antibody became detected in controls exposed to an infected environment. Although the antibody positive rate did not exceed 50% even at 8 to 14 weeks of age in mice weaned at a time when thepositive rate of retired breeders was comparatively high, the positivity reached 60% or more at age of 8 weeks or older but none of them died, when 4-week-old mice from a non-infected colony were housed in the infected one. Germf ree mice of 3 or 4 weeks of age directly or indirectly associated with feces of 5-week-old mice from the infected colony died at mortality of 25 to 64% and most of the survivals were shown to have antibody after one month.

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The growth and the survival after transplantation of tumor cells were compared between mice kept in wire-mesh cages (16×28×12cm) (Fig.1) and mice kept in polycarbonate cages with wood shavings (18×27×13cm) (Fig.2) . ICR-JCL and ddY-SLC mice of both sexes were kept separately 5 each in a cage, maintained in an airconditioned animal room (26±0.5°C and 60-70% in relative humidity) artificially illuminated (12h light from 8: 00 AM to 8: 00PM), and they were provided with commercial diet (CE-2 : CLEA Japan Inc., Tokyo) and wateras libitum. Individual body weight was measured every 10 days during 30-140 days of age. Thereafter, about 10⁷of living cells of asci tes sarcoma 180 and Ehrlich ascites carcinoma were transplanted subcutaneously and survival days were checked. There were little differences in the growthexcept male ddY-SLC mice of which body weights after 90 days of age were significantly heavier in wire-mesh cages than in polycarbonate cages (Figs. 3 and 4) . The survival days after transplantation of tumor cells were not different between mice in wire-mesh cages and those in polycarbonate cages in either sex of both ICR and ddY mice (Table 1) . These results indicate that a wire-mesh cage is useful without disadvantages for maintenance of mice, especially in automatic or labor saving systems.

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[in Japanese]

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