The effect of population density on the growth and the reproduction was studied, using ss strain of mice for the experiment. The animals were raised from their birth in different numbers (4 and 8 heads) in cage of the same inner dimensions and their growth, sexual maturity and reproductive ability were studied in comparison. The litter size was limited to 4 youngs (sex ration= 2: 2) and in the low-density group of 4 heads per cage, one such a litter was reared, while in the high-density group of 8 heads per cage, two litters were kept in one cage, in company with their mothers for 30 days after birth. The fallowing differences in the results were found between the two groups.
Growth: The growth of the animals in the low-density group by 60 days after birth was markedly better than that of the animals in the high-density group.
Age of first conception of female mice: 51.1 days on the low-density group and 84.8 days in the highdensity group.
Age of descent of testis: 28 days in the low-density group and 39 days in the high-density group.
Reproductive ability: In the low-density group, the litter size averaged 6. 78, the litter weight 8.44g and the birth weight 1.29 g, while in the high-density group, the mean values were 6. 11, 7.48 g and 1.23g respectively.

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Litters of newborn ss strain of mice were limited to 4 youngs per litter and were reared in cages of different inner dimensions together with their mothers. The results of comparative study of the development of the groups were in summary as follows:
Growth: The growth was the better, the larger the cage, the difference in the pace of growth becoming perceptible by 30 to 40 days after birth.
Age of eye-opening : Was particularly early in the animals kept in the largest cage (9 days), but in the her cages, there was found no difference, the eyes being opened at the age of 12 or 13 days.
Age of sexual maturity of female mice: No difference in the date of opening of the vagina was perceptible but the date of first conception was the earlier, the larger the cage in which they were reared.
Age of descent of testis: No significant difference was found in this respect.
Reproductive ability: No correlation was established between the size of the cages and this ability.

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Studies on the stability of the vitamin B complex in“Oriental compressed diet” which is available for mice, rats (M, NM) and rabbits of vitamin B complex in the diet were examined and most suitable method of analysis for each vitamin was selected. The analysis were immediately after preparation of diet and also after its preservation for 12 months at 0-4°C, 20-26°C, 29-31°C and 36-38°C
The results were as follows:
1) Vitamin B content was found to be satisfactry for the requirement of each kind of laquirement of laboratory animals.
2) Content of vitamin B complex decreased very little and was maintained well for 12 months, as far as diet was controled at about 7 % moisture.

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To clarify the mechanisms of infection and immunity of mouse typhoid, an experiment was carried out using several strains of mice. A highly virulent strain of Salmonella enteritidis was used as an infective agent. The strains of mice used were C57BL/6, CF#1, CFW, ddN, SM and dd/Ks strain. The last strain is an inbred one raised in our laboratory from one parent of ddN mouse by full sib-matings and selecting the mice highly susceptible to the infection with S. enteritidis. The results obtained were as follows:
1) C57BL/6, CF#1 and dd/Ks strains were uniformly highly susceptible to the intraperitoneal infection with S. enteritidis, but CFW, ddN and SM strains were not so susceptible as the former three strains.
2) To the intrastomachal inoculation with S. enteritidis C57BL/6 and dd/Ks strains were as susceptible as to the intraperitoneal infection, but CE#1 strain, though it was highly susceptible to the intraperitoneal infection, showed only a low degree of susceptibility to the intrastomachal inoculation. CFW, ddN and SM strains showed nearly the same low grade of susceptibility to the intrastomachal inoculation as to the intraperitoneal infection.
3) The acquired immunity with heat-killed vaccine to the intraperitoneal infection could not be attained by C57BL/6 and dd/Ks strains that were both highly susceptible to the infection, but in CF#1 strain a fairly good state of immunity was attained despite its high susceptibility to the intraperitoneal infection. CFW, ddN and SM strains that were not so susceptible to the infection attained a good state of immunity to the intraperitoneal infection by the inoculation with heat-killed vaccine. An attenuated live vaccine conferred a fairly good state of immunity on all the strains.
4) No correlation between the grade of antibody response to the vaccine and that of immunity to the infection could be observed.
5) The peculiar attitude shown by CF#1 strain in the intrastomachal infection and in the immunity experiment with heat-killed vaccine was discussed as follows considering the course of the infection. In the course of mouse typhoid there would be two major streams of infection, one would be bacterial multiplication in septic form and the other would be bacterial multiplication in the organs in which the infected bacteria resided. If the high susceptibility to the intraperitoneal infection of CF#1 strain was due to the septic bacterial multiplication rather than the bacterial multiplication in the organs, the effect of heat-killed vaccine in CF#1 strain would be conspicious, because very effective prevention with heat-killed vaccine against the septic bacterial multiplication had been observed in our study described elsewhere. Furthermore the low susceptibility to the intrastomachal infection of CF#1 strain could be explained by the same assumption, because the major determinant of the outcome of the intrastomachal infection would be the bacterial multiplication in the organs which would be less sevire in the infection of CF#1 strain.

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Investigations were made on the response of various kinds of small experimental animals to per os, subcutaneous, and intratesticular infection withBrucella abortus.
All the animals tested were found to be susceptible to the infection with Brucella abortus irrespective of the route of inoculation and the reactions observed were principally of the same nature. Intensity of the reactions, was the strongest with the guinea pig and that of the mouse was much weaker confirming the findings reported before.
Hamster, cotton rat (Sigmodon hispidus), mongolian gerbile (meriones unguiculatus), and Japanese maedou-mouse (microtus montebelli), which have never been subjected for experimental infection with Bruccella abortus, gave the same reactions as those observed with mouse.

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Surveys were made in order to eliminate the use of contaminated eggs for the production of fowl pox vaccine. For, in the case of fowl pox vaccie, emulsions with a bacterial count over 100 colonies per cc and those withSalmonellacontamination are not acceptable as vaccine.
Fertile eggs were collected from 3 different poultry farms A, B and C, and subjected for the survey.
Large numbers of the eggs collected from A and B farms died in the middle of hatching and many of the emulsions made with the servival embryos were also found to be heavily contaminated with bacteria. Moreover, though the number was small, there were some emulsions contaminated withSalmonella.
On the other hand, the survey made on the fertile eggs from C farm showed that the number of embryos died while under hatching as well as contaminated emulsions were very few. In addition, there was not a single case ofSalmmellainfection.
Pullorum agglutination tests were made on the hens (1-2 years old) of the same farms. As the result of this investigation, the number of positive reactors was extremely high in A and B farms, while it was very low in C farm.
Namely, it is considered that there is a proportional correlation between the number of died embryos or contaminated emulsions and the number of hens infected with pullorum.

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