Skeletal variations in the various strains of mice (C57BL/6HeMs, CF#1, RF, and C3H/AnHeMs) and their F1 hybrids which were produced by reciprocal crosses of three inbred strains (C57BL/6, CF#1, and RF) were demonstrated. These strains were bred and maintained by the sister-brother matings since 1960 in the Natonal Institute of Radiological Sciemces. Examined bones are followings: interfrontal bone, cervical vertebrae, thoracic vertebrae and ribs, lumber vertebrae, sacral vertebrae, and caudal vertebrae. The same analysis was carried out further with the ICR-JCL mice which were bred and supplied in the Central Laboratories for Experimental animals. The data obtained were presented in Table 1-6.
Frequency of “interfrontal bone” was higher in C57BL/6 and RF strains (about 27%), and lower in others. The cervical vertebrae were 7 in all strains and their F1 hybrids. The fusion between cervical vertebrae (other than atlas-axis fusions) was seen frequently in the C57BL/6 (31% in all specimens of the C57BL/6), but none was found in ohers. Variations in thoracic vertebrae and ribs were found in CF#1 (17%), RF (7.1%), and ICR (6.1%) . These variations included the 13¹⁴, 14¹³, and 14 thoracic vertebrae (i. e. rib-bearing) . Other strains of mice kept always 13 thoracic vertebrae without variations.
The lumber vertebral numbers of C3H, ICR, and RF were predominantly 6. On the other had, the mice with 5 lumber vertebrae were appeared in the C57BL/6 (20.5%), CF#1 (13.8%), (C57BL/6 × CF#1) F1 (15.3%), and (C57BL/6 × RF) F1 (11.1%) with compared to the other strains and their F1 hybrids.
Two types were obseved with the pattern of sacral vertebrae : 4 bone-fused type and 3 bone-fused one. The former was found in the CF#1 (100.0%), C3H (96.5/), RF (94.4%), and ICR (67.7%), the latter was found frequently in C57BL/6 (58.9%), and the F1 mice from C57BL/6 males and females. Caudal vertebral numbers of the adult mice were distributed between 27 and 35. The largest numbers were found in the ICR and the smallest were observed in the C3H and C57BL/6 strains of mice.

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Since 1959 an effort has been made in order to establish a mouse strain characteristic of frequent spontaneous alveolar formation in mammary gland of virgins.
Full-sisters were kept in a cage from weaning to the day of mammary gland examination, exposed to male odour. On the basis of examination on mammary gland biopsied in females and of progeny test in males, one pair was selected at the latter half of 1961.
Descendants from them formed two groups, one showing 74.3%, the other 54.8% of the spontaneous alveolar formation in mammary gland at 10-14 weeks of birth. Further descendants from the two groups subjected to successive selection exhibited 49.7% of the formation at 11 weeks of birth.
The reason why they exhibited the spontaneous alveolar formation is not yet determined but the formation may be caused by the hormones secreted mainly from corpora lutea of ovary, indicating an extra coital pseudopregnancy.
Discussion was made on the factors contributing to the establishment of the mouse strain and also on the utility of mice with the spontaneous alveolar formation.

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[in Japanese]

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It is very important for the prevention of Polyoma virus infection to study on the effect of aseptic agents on this virus, and this is clear from our article “On the Handling of Polyoma Virus” which has been published before in this Journal (Bull. Exp. Anim., 11 (3) 130. 1962) . To clarify this problem we have examined the effect of several kinds of drugs, which are generally used, on the Polyoma virus in vitro. Six aseptic agents, namely cresol, sodium hypochlorite, phenol, benzalkonium chloride, benzethonium, chloride, and alkyl polyaminoethyl glycine chloride have been studied and it is clarified that the cationic soap especially benzalkonium chloride is most effective and cresol or alkyl polyaminoethyl glycine chloride is slightly effective. By using 1/500 of lOw/v% benzalkonium chloride in vitro at room temperature for 30 minutes the infectivity and hemagglutination of Polyoma virus (TCID₅₀: 10_3.25) are completely inhibited.

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