The influence of environmental temperature on the susceptibility of ICR-JCL mice in terms of mortality, when exposed to the three environmental temperatures; 10, 25 and 35°C, for 24 hours each before and after an intraperitoneal injection of pentobarbital, adrenalin or acetylcholine was studied. In addition, physiological variables such as the electrocardiogram, heart rate, respiratory rate, blood pressure and body temperature were observed in the mice after injections at each of the three temperatures mentioned above.
1. The susceptibility of mice to the toxicity of pentobarbital in terms of mortality was highest at 10°C and lowest at 35°C. As a rule, the heart rate and respiratory rate as compared with the control animals decreased after pentobarbital administration. This was more marked as the environmental temperature was lowered. The drop in body temperature as compared with that in the control group in mice exposed to 10°C or 25°C, was more marked than that in the animals exposed to 35°C. The drop took place gradually but consistently. Changes in the blood pressure resulted mainly from injection of the drug, and were not caused by changes in the environmental temperature.
2. The susceptibility of mice to the toxicity of adrenalin at 10°C was higher than that at 35°C This susceptibility was higher at 35°C than at 25°C. When an overdose of adrenalin was administered, the heart rate decreased gradually but consistently, though the respiratory rate and blood pressure increased once momentarily and then decreased. The body temperature dropped gradually but consistently. These functional changes were greater at 10°C than at the other temperatures, though they appeared most rapidly at 35°C after the exposure was begun.
3. The mortality of mice after an injection of acetylcholine was the highest at an environmental temperature of 35°C, and the mortality at 10°C was somewhat greater than at 25°C. Arrhythmia was commonly observed in almost all cases after administration of acetylcholine in a dose of 25mg/kg or more. The heart rate and blood pressure decreased temporarily during the early period after injection of the drug. The respiratory rate and body temperature decreased gradually. Inhibition of these physiological functions after administration of acetylcholine in a dose of 120mg/kg was most drastic when exposing the animal to 35°C, followed by the death of the animal within about 7 minutes. At 10°C the effect of the drug was once compensated for and then decreased gradually.
On the basis of these experimental results, the importance of regulating the environmental temperature during experiments in regard to toxicity of a drug, for example, is evident.

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Since January, 1958, a subline of C3H/He mice (Dr. Heston, N. I. H.) has been introduced at the Institute for Cancer Research, Osaka University Medical School. This strain has been continued by brother-sister mating and at the present, November, 1966, has reached the 37th generation. Old male mice develop spontaneous hepatomas as high as 34%, and females have a high incidence of spontaneous mammary tumors (92.5% for breeders, at 35.9 weeks in average and 78.8% for virgins at 46.1 weeks in average) . Detailed data of occurrence of the mammary tumor of this strain from 18th to 30th generations have been listed for comparison of related C3H sublines of mice such as C3H/He, C3H/HeNSa, C3H/An, and C3H/Bi. It has been proposed that this strain of mice has been established as a subline of C3H/He and that from now on we designate this strain of mice as C3H/HeOs.

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In order to breed mice and rats in healthy conditions, a small animal room was designed as follows.
When a fan F works every 15 minutes by the control of a timer C, cool air from a neighbour aboratory comes into the animal room through a duct D attached on the door, and disperses after warming by a heater R 2 which works simultaneously with F. Further fine regulation of the room temperature is made by another heater R 3 and regulator B; thus the room temperature is kept constantly as shown in Fig. 2. Ammoniac gas and bacteria were scarcely detected in the room.

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An attempt was made to check with retired breeder mouse sera, Corynebacteriosis, Salmonellosis, Tyzzer's disease and infections due to mouse hepatitis virus (MHV (Pr) ) and Sendai virus. Of 1, 530 sera collected in March and April 1967 from 13 commercial and institutional breeding colonies, 5 (0.3%) and 19 (1.2%) were shown to have antibodies to Tyzzer's agent and MHV (Pr) respectively by complement fixation test with each infected liver antigen. Of 1, 338 sera of mice which had not received Sendai virus vaccine, 305 (22.7%) showed positive CF reaction to the virus antigen, and in some colonies more than 80% of mice were found to be infected with this virus, In these colonies showing a highly epidemic pattern, respiratory disorders were noticed clinically and pneumonia was observed frequently at autopsy. Agglutinin against Corynebacterium kutscheri was detected in 112 of 1530 (7.3%) sera at high titers, while the antibody against Salmonella enteritidis was demonstrated only in 2 sera of a single colony. In many of mice showing positive serology to Corynebacterium antigen were detected severe lesions as gross abscess in the liver, kidney and lung as well as purulent nephritis.

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