This experiment was made to observe the relations between the number of ova and the litter size in different strains of mice.
The mice used were CFW, CF#1, C3H, C57BL, SS, AA and KK strains, approximately 90-120 days of age, which had been raised under the same conditions since birth. The number of ova discharged by ovulation was calculated from the ova in the ampulla of the uterine tube of mice in which the vaginal plugs were observed. The average number of the ova, the litter size and the survival rate of the young (the proportion of the newborn youngs to the number of ova) were compared among the different strains of mice.
The results obtained were as follows.
1) In the each. strain of mice, when the number of ova in the left ampulla and the right ampulla of the uterine tube were compared, there was no statistically significant differences between the number of ova in the left ampulla and the right ampulla of the uterine tube.
2) The strains which showed a larger number of ova were CFW, CF#1 and SS (average range 11-13) ; a medium value was shown in C3H, AA and KK (average range 10.0-10.7) ; and a small value was shown in C57BL (average value 8.8) . There were statistically significant differences in this number among CFW and C3H, C57BL, SS, AA, KK ; among CF#1 and C3H, C57BL, SS, AA, KK ; and between SS and C57BL.
3) The strains which showed a large litter size were CFW and CF#1 (average range 10-12) ; a medium value was shown in SS, AA and C57BL (average range 7.4-7.9) ; and a small value was shown in C3H and KK (average range 4.7-5.2) . There were statistically significant differences in this number among CFW and C3H, C57BL, SS, AA, KK ; among CF#1 and C3H, C57BL, SS, AA, KK ; among SS and C3H, KK, among AA and C3H, KK ; and among C57BL and C3H, KK.
4) The survival rate of young was 83-93 per cent in CFW and C57BL; 70-77 per cent in CF#1, SS and AA; and 43-50 per cent in C3H and KK.
5) From these results, it was found that there was no parallel relationship between the number of ovaand the litter size in the different strains of mice and it was concluded that the litter size was determined not only by the number of ova dis charged from the ovary of the dam, but also by the many other factors. The factors determining the litter size were discussed.

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The susceptibility to audiogenic seizure under the pure sound stimulation was observed to investigate the influences of noise on laboratory mice.
Laboratory mice from eight inbred strains (BALB/c, C3H/HeN, C57BL/6, DBA/2, CS, DDD, KK and NC) and two closed colony stocks (ICRJCL and ddN-JCL) were used : a total of 586 male and female mice aged from 3 to 4 weeks old. These mice were observed for strain and sex differences. In addition, distribution of susceptibility according to age was observed : a total of 306 female ICR-JCL mice aged from 1 day to 8 weeks.
Sound stimulation was effected by pure sound in the 6, 000 to 20, 000 cps frequency range and 70 to 120 decibel intensity range in a soundproof box.
On receiving the sound stimulation, the mice exhibited various types of abnormal behavior suchas surprise, momentary freezing, wild running, uncontrolled-circling and finally convulsion. The susceptibility to audiogenic seizure was decided by whether the convulsion was fatal or nonfatal. All these observations were based on initial exposure of each mouse to the sound stimulus.
The results are summerized as follows
1. Audiogenic seizure occured at sound frequencies from 6, 000 to 18, 000 cps at a 110 decibel-constant intensity, with the peak close to 10, 000 cps. The susceptibility to intensity at a 10, 000 cps-constant frequency appeared from 80 decibels, and increased as the intensity increased.
2. Susceptibility according to age was the highest in the female ICR-JCL stock from 3 to 4 weeks old.
3. Susceptibility to audiogenic seizure according to strain was obvious. The DBA/2 strain was most susceptible, ddN-JCL and ICR-JCL stocks were in middle, while DDD and C57BL/6 strains were low. Other strains (BALB/c, C3H/HeN, CS, KK and NC) were all resistant.
4. Susceptibility according to sex was slightly higher in males than females, but not significantly.

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An attempt was made to check corynebacterial infection in rats from conventional commercial sources by cortisone treatment and the results are summarized as follows :
2. In cortisone-treated animals, necrotic and purulent lesions were observed frequently in the liver, kidney, heart and lung as well as the digestive tracts, whereas the organs other than the lung were involved much less frequently without cortisone-treatment.
3. Organisms isolated from liver lesions of cortisone-treated rats showed similar morphological and biological characteristics as those of
1. The infection was checked effectively by daily injections of 5 mg cortisone acetete intramuscularly for 10 consecutive days into 5- to 6-week-old rats weighing 59 to 117g.
Corynebacterium kutscheri isolated from mice and they were agglutinated with rabbit immune serum against C. kutscheri.
4. After intraperitoneal inoculation with the isolated organisms rats showed multiple necrotic and purulent lesions in the lung, liver, kidney and heart and these lesions were found to be aggravated remarkably when cortisone treatment was combined with the inoculation.

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