During the period from 1957 to 1959, many strains ofBord. bronchisepticawere isolated from the guinea pigs used for the safety test of biological products. Particularly, from winter to spring, the organisms were frequently obtained, but neither significant symptoms nor death was observed among these infected guinea pigs.
In regards to feeding and administration of laboratory animals, however, it is no doubtedly important that guinea pigs should be controlled against these quiescent infectious agents.
From the results of our inoculation test, in which guinea pigs were inoculated intranasally with the fresh culture ofBord. bronchiseptica, or with the emulsion of the locus of pneumonia of guinea pig, we have confirmed thatBord. bronchisepticawas a causative agent of the pneumonia described here.

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In animal experiment, it is necessary that the factors which exist and might act an important role in the purpose of the experiment, should be studied initially according to the purpose of the experiment.
The authors have made an experiment to investigate whether the lethal dose of the snake venom for mice might be affected by the factors such as body weight, sexes of the mice and the route of the inoculation using five strains of mice derived from distinct sources.
As to the relationship between lethal doses and strains of mice, the response of gpc/Y for the venom was the same as that of dd/Y, and especially the strain gpc/Y was regareded as comgaratively homogeneous, since the responses of the strain were found quite similar in repeated observations.
There was no significant difference statistically between gpc/S and dd/S, and gpc/Y and dd/Y in the results obtained. But the susceptibility of the former group (gpc/S and dd/S) was slightly different from the latter, and also some tendency of fluctuation was noted among the results obtained from that group.
Toxicity for mice in connection with the body weight and sex of mice was as follows: LD50 of the venom for mice did not seem to be influenced by the body weight which was within the limit of 14 gram to 17' gram either in gpc/Y and gpc/S and no appreciable difference was seen between each sex as such size of mouse was employed.
However, the LD50 of the venom was affected remarkably by the route of the inoculation. Almost equal results were obtained either from intravenous or intraperitoneal inoculation, while mice resisted firmly to subcutaneous as well as to intramuscular inoculations. The subcutaneous and intramuscular inoculations are hardly regarded as highly accurate methods as their confidence limits of the LD50 are so wide. On the consideration of the results mentioned above, it may by concluded that the subcutaneous and intramuscular inoculation methods are inadequate to estimate the lethal dose of the snake venom for mice.

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Inbred mice (ss-strain and dd-strain) and their F₁ (ss x dd-F₁ and dd x ss-F₁) were fed under high and low denisities of breeding and their growth and ability of reproduction were compared each other among these groups.
In bodily growth, the hybrids grew better than the inbreds regardless the population density. The inbreds showed better growth under lower density of feeding, however the hybrids showed little inequality in growth by different population density.
The age of saturation in day in female mice under low breeding density was younger in ss-strain of mice than that in dd-strain, however little differenfwas found between the inbreds and hybrids in the age of maturation. Under high population density, the dd-strain female mice showed earlier maturation than ss-strain. These findings probably suggest that the ss-strain mice are more keenly sensitive to the change in population density. The hybrids always showed earlier maturation than the inbreds. Under different densi-ty of feeding, the inbreds generally matured earlier under low density, the hybrids showed little difference in this respect. The hybrids matured earlier even under high population density than the inbreds fed under low density.
The litter size generally tended to be larger in hybrids, whatever populatin density was. The total weight of a litter also showed the same tendency. The avarage weight of newborne of inbreds was found larger than that of hybrids under lower population density, whereas it was smaller under higher population.

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