Contaminations with various species of bacteria were occasionally observed in guinea pigs before or after the safety test of biological products.
The response in bodyweight of carrier, guinea pigs, was so irregular that it was difficult to decide on the results of test.
In the case of quiescent carrier state, such as Bord. bronchiseptica and Citrobacter infections, the increase in bodyweight of guinea pigs in the safety test was generally similar to that of normal guinea pigs, but sometimes either death or irregular growth was experienced.
In the case of furious carrier state, such as Strep. hemolyticus and S. typhi murium infections the increase in bodyweight of guinea pigs became irregular after the inoculation of biological products.
Accordingly, in the experimental study of laboratory animals, usually one must have the knowledge of ecological state of those laboratory animals.

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In the fall of 1956, the authors happened to recognize the occurrence of minute nodules in the livers of the mice, which were borne in their colonies. The incidence continued sporadically, until they had been able to diagnose it as the “Tyzzer's disease” in October 1958. It was presumed that the source of the contamination could already exist when the breeding of their colonies was started in 1952.
The autopsy of the infected mice revealed no significant differences in either the strains and sexes of the animal or seasonal prevalences of the disease.
Experimental infection of the mice by oral route employing the material derived from infected liver was not successful. However the intravenous inoculation accompanied with subcutaneous administration of cortisone, or the intracerebral inoculation were able to infect the mice consistently, so that the serial passage of the agent has been carried out by either route.
Histopathological changess of the infected liver and the stability of the agent in the emulsion of the infected liver were studied using both routes of inoculation.
Aureomycin, suspended and given orally in the water to the mice appeared to be somewhat effective for the prevention of the experimental infection. Among several sorts of the vaccine, prepared from the infected mouse liver, only the formalinized-concentrated one was slightly effective to protect the animal from death though it could not prevent the pathologic changes in the liver.
The detection of the potentially infected parents by the autopsy of their litters was proven to be the useful device rather than sacrificing the parents from practical point of view. Subsequently, this method was employed for the evaluation of the prophylactic effects of kureomycin and or vaccine upon the incidence of the disease among the colonies of the mice. No meaningful difference was noted between control and recipients. Eventually, the disease was completely diminished by the effort directed toward the careful detection and the successive isolation of the infected parents.

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Meriones unguiculatus Kurauchii Mori were bred, and their duration of pregnancy, size of litters and some postnatal developmental changes of the young were examined. The principal results may be sum-marized briefly as follows :
1. The duration of pregnancy was found to be 24 to 26 days.
2. Average number of a litter was 4.8±0.9. The value of the first litter was the lowest.
3. The growth curve of the body weight was nearly S-shaped and in general, the female was slightly inferior to the male.
4. The tail ratio was lower than that of rats at the time of birth, but it increases remarkably during maturation.
5. As for the external developmental changes, the opening of the ear auricle and the eruption of the lower incisors occured in the period similar to rats or mice, while the opening of the eyelids was observed few days later than that of latter animals.
6. The testis descended in average on the 36 th days of age, while the vagina opened in average on the 49 th day.

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1. Repeated immunizations with heat-killed as well as chrome alum-treated vaccines of Salmonella enteritidis failed to produce marked immunological responses in young mice of less than 20 days old. Circulating antibody titers were found to reach high levels eventually as the animals gradually matured.
2. On the other hand, a prenatal inoculation of the vaccine administered to fetus mice evoked neither the transitory depression of immune response nor the permanent tolerance against the specific antigens.
3. Statistical analyses were made with paper electrophoresis of sera taken from young mice at various times during the first 6 weeks of life; the neonatal high gamma globulin level dropped after birth, reaching the lowest levels at 3 to 4 weeks, followed by a slow rise up to 6 weeks of age. The serum albumin contents increased significantly during the experimental period, whereas alpha plus beta globulin remained at the same low level throughout the period.
4. The fall in gamma globulin level in early life was, then, compared with the rate of disappearance of passively administered homologous antibodies. It was tentatively concluded that even though the total amount of gamma globulin was decreasing in newborns there must be a small quantity of new gammaglobulin being formed at the same time.
5. A reasonable conclusion may be that the most probable cause of the poor antibody formation in young mice can be ascribed to the immature ability of the animals to produce new gamma globulin.

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