Using the respiratory apparatus based on air current method, the present experiments were made on some factors which appeared to influence on the gaseous metabolism of mice and the following results were obtained. 1) For collecting the respiratory air in the sampling chamber it may be suitable to use liquid paraffin and the saturated solution of sodium chloride. 2) Gaseous metabolism rised with three steps by the increase of the flow rate of inlet air, though the plateau value range in gaseous metabolism was observed between the first and the third steps. 3) Gaseous metabolism decreased follow with the rise of the temperature from 20°C to 30°C in water bath surrounding the animal chamber. 4) Gaseous metabolism also decreased folling with the growth of animals (15 to 57 days after birth), among the strains of CF#1, RF, and CRF1 mice, the gaseous metabolism of RF mice showed higher value than that of other two strains at 15 days after birth, but it was not significantly different at 37 days or over between RF and other two strains.

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The mice studied were of male and female C 57 BL/6, male and female CBA, male and female CF #1, male dd/YF and male ICR/JCL at the age of fifty days. Fifty mice were choiced for each sex and each strain from the data of repeated experiments for various purposes, according to the age, sex, strain and housing condition in our laboratory.
The distribution of body weight at the tenth day after putting into an individual cage from other cages showed a single or more lines on the logarithmic probability paper. The distribution of the mean square successive difference induced from the daily body weight for ten days in the individual cage, showed three lines on the logarithmic probabiity paper, except two lines for female C 57BL/6mice. The mean square successive difference expressing the physiological state of individual mouse, those three lines showed that the population of mice was divided into three groups of mice with three types of phisiological states probably due to long-conditioning stimulus. These types showed different responses against whole body irradiation. Studying on the mean square successive difference induced from body weight, it was noticed that the effect of removing mice from a cage to another one remained for ten days at least, since the value was unstable till the ten days.
Figure 1 Distribution of body weight in various strains and sexes of mice. Mice were housed separatly in an individual cage for ten days and weighed at the tenth day.
Figure 2 Distribution of mean square successive difference (δ2) induced from body weight of various strains and sexes.
Mice were housed separately in an individual cage for ten days and δ2 was calculated from the daily body weights for ten days.
Figure 3 Changes in body weight and in mean square successive difference induced from body weight in every successive two days after putting the mouse into an individual cage. Mice C57BL/6 mice at the age of fifty days were weighed at 10: 00 a. m. for ten days in the individual cage.
Table 1 Survival at 30 days after 400 R whole body X-ray irradiation. Mice dd/YF mice were irradiated at tenth day after putting into an individual cage separately.

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Animals are thought to be suitable for experiment, when following criteria are fulfilled: 1) The animals should either respond to a given stimulus markedly or remain without reactions. 2) The indications before treatment never show the great individual difference. 3) The indications after treatment never show the great individuality as well.
Firstly, responses to a treatment may be conjectured by Tukey's or Scheffé's method. Secondly, the stability of indications before treatment are given by coefficients of variance. The smaller the coefficient, the more uniform the indication.Finally, the uniformity of the response to a given stimulus is examined with the following formula :
√V_{B (P)} /X
where
V_{B (P)} =unbiased variance among individual animals
X=arithmetic mean
The smaller the value, the uniform the response.
The method of selection of animals for experiment, as well as the determination of its critical parameters and the administered dose, are given as an example of benzene poisoning. And mature rats of Sprague-Dawly strain were found the most suitable animals for the experimental work in benzene poisoning.

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