A female mouse showing opacities of the lens in both eyes, was first found in ICR-JCL mice from the colony of the Nihon CLEA Co. Ltd., Tokyo, in February, 1966.
From extracted progeny of this animal, a stock has been established in which all the animals are defective; cataract combines with microphthalmia.
The genetic analysis showed that the mutant condition is probably caused by a single autosomal semi-dominant gene. The term “small eye and cataract” (gene symbol Cs) is proposed for the mutant, since this describes the characteristic appearance of eyes in homozygotes.
In the Cs/+ heterozygote, either one or both eyes shows opacity of the lens, but the lens itself is normal in size. While the Cs/Cs homozygote shows a similar cataract condition to the heterozygote, but the lens is about one-half the size of normal or heterozygote one.
When the mouse has opened its eyes, a milky white spot is easily visible in almost of the affected eyes ; it corresponds probably to an aggregation of homogeneous masses from dead lens fibrils.
More detailed histopathological and developmental experiments are still in progress.

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The use for obtaining hypothermia in mice and the growth pattern of lipovirus in the hypo-thermic mice were studied. The results are summarized as follows :
1) The intraperitoneal administration of chlorpromazine and barbital sodium resulted in a low body temperature which persisted only for 10 to 30 hours. Even after repeated administration of the drugs, the hypothermia could be hardly maintained for a longer time period.
2) Under the environmental temperature of 4°C, however, the body temperature of mice fell to about 31°C but recovered to about 36°C 2 days later. And, since the 8th day of the exposure to the cold environment a stable hypothermia which was 1.5 to 2.0°C lower than the normal body temperature of mice was established.
3) Lipovirus showing an optimal temperature of growth at 33°C in vitro and no significant growth in normal mice, was found to propagate and to cause pathological changes in hypothermic mice kept at the environmental temperature of 4°C.

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Genetical discussions for maintaining inbred strains have been reported many times, but there have been few papers concerning closed colonies of mice. To maintain a closed colony, it is important to consider two factors. The first is the increase of the inbreeding coefficient, which is related to changes in gene frequencies or changes in genetic components which affect biological reactions. If the inbreeding coefficient is increased, experimental results are changed with respect to those of previous experiments because of changes in the genetic constitution of the colony. The second factor is the occurence of subdivision in the colony. If a subdivision occurs in a colony, two groups of mice derived from different parts of the colony will have different genetic characteristics.
When we maintain a closed colony of mice, we must always know the degree of inbreeding and occurence of subdivisions, and try to prevent them as much as possible.
Two closed colonies, an ICR-JCL colony and a CF#1-JCL colony, were maintained in our Institute. These colonies have been maintained by a breeding system kown as the “rotation system for noninbred” consisting of three groups (A, B, C), as shown in Fig. 1. For example, the mating pairs in group A in a new generation are made up of virgin males and females supplied from group B and C, respectively, and so on. The ICR-JCL colony is maintained by breeding about 225 males and 1350 females, and the CF#1-JCL colouy by breeding about 50 males and 300 females in each generation.
In order to investigate the inbreeding coefficient and the index of subdivision in these colonies, 500 pairs from actual mating of a generation in the ICR-JCL colony and 200 pairs in the CF#1-JCL colony were sampled randomly (instead of sampling individuals from the progeny population) . The total inbreeding coefficien (F) and the inbreeding coefficient (F') from the inter-se relationship (R) were estimated by Wright and McPhee's method.
In the ICR-JCL colony, the total inbreeding coefficient (F) was estimated as 0.007 on two and half years and about six generations after we started to breed this colony ; and in the CF#1-JCL colony, it was estimated as 0.038 after two years and about five generations, as shown in Tables 1 and 2. The total inbreeding coefficient in the ICR-JCL colony was less than in the CF#1-JCL colony maintained with a smaller number of breeding individuals.
The inbreeding coefficient (F') from the interse relationship was estimated as 0.014 and 0.039 and the index of subdivision. (F/F') was 0.502 and 0.963 in the ICR-JCL and CF#1-JCL colonies, respectively. Since the values of the indices of subdivision are less than 1, no subdivision actually occurs in these colonies.

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Some investigations were carried out on airborne bacteria in different parts of laboratories. The results are summarized as follows:
1) The numbers of air-borne bacteria were much different among animal rooms under different conditions. (Fig. 2) .
2) Bacterial number in the experimental room attained its maximum at daytime and its minimum at night (Fig. 5) . The mean number of air-borne bacteria in animal room however, was larger at night than at daytimes (Fig. 4) . The daily changes of bacterial number in the vestibule were similar to those in the experimental room (Fig.3) .
3) The numbers of bacteria in animal rooms before and after introduction of animals was considerably different. (Fig.6 & 7) .
4) The numbers of air-borne bacteria in the animal rooms differs with the species of animals. The highest contamination was observed in the rabbit room.
5) The difference in number of bacteria between the levels of 170 cm and 20 cm distant from the floor was obserbed (Fig. 6 & 7) .
6) Over 90 per cent of the contaminated bacteria were of underf fined micrococci, and the rests were of diphtheroids, coliforms and fungi (Table. 2) .

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