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Twenty-six out of fifty pregnant rats died on days 18-20 of gestation at 33 degrees C environment. The death generally occurred in the dark period around 1-5 a.m. Shortly prior to the death, very high body temperature of 42.0-43.7 degrees C were recorded and the blood pressure was undetectably low. In autopsy, the finding in the main was the congestion in lungs and liver. In temporal changes of body temperature and heart rate, influences of hot environment were observed, but there was no significant difference between dead pregnant group and delivered pregnant group at 33 degrees C environment. At 23 degrees C, the blood pressure of pregnant rats starting at about 140 mmHg level, reached 160-168 mmHg on day 12 of gestation and maintained the level to day 16. On day 18, the pressure returned to 140-145 mmHg and unchanged to term. At 33 degrees C, significant differences were obviously observed between dead group and delivered group in temporal changes of blood pressure. The blood pressure of rats delivered sharply increased to 170 mmHg or more in the middle stage of pregnancy and decreased to about 140 mmHg in the final stage. However, these of dead group increased to 160 mmHg or less in the middle stage of pregnancy, and maintained the level until the final stage.

The relation of the rate of circulating air change to room temperature and relative humidity in animal quarters with a central air-conditioning system during heating and cooling seasons was investigated, with the results as follows: During the period of heating, the ambient temperature generally rose with a fall of relative humidity as the number of conditioned air changes per hour was increased. Vertical differences in temperature and humidity between levels of 0.5 and 1.5 m above the floor also diminished with increasing air change rate. This tendency was more conspicuous in small animals rooms with outer walls facing north and west. With increasing rate of air changes, the room temperature was prone to decline and the relative humidity to rise during the period of cooling. There were less vertical differences in temperature and humidity during this period. The velocity of air circulation within the animal quarters and its variations tended to increase progressively with increasing rate of ventilation, though the changes were modest.

Two consecutive generations of mice were raised at graded room temperatures ranging from 12 to 32 degrees C at intervals of 2 degrees C. The delivery rate decreased at 30 and 32 degrees C, and the litter size and weaning rate decreased above 28 degrees C. No significant difference was demonstrated within the 12-26 degrees C range for any reproduction parameters observed. The body weights of the first-generation mice born at 22 degrees C and transferred to rooms at assigned temperature did not significantly differ within the 14-28 degrees C range after 8 and 16 weeks of exposure. The second-generation mice born and reared at various temperature levels did not show significant inter-group difference in weight within the 20-26 degrees C range at any age in the growth period. No significant inter-group difference was observed within the 20-26 degrees C range in respect of food and water intakes in the second-generation mice. Hematological values and organ weights in the first and second generation mice of both sexes did not significantly differ in any parameter within the 20-26 degrees C range. The results suggest the temperature range of 20-26 degrees C to be optimal for laboratory mouse rooms.

The relation between blood pressure and delivery in pregnant rats was investigated when the blood pressure of pregnant rats was controlled by a pressor or antihypertensive drug in the middle or final stage of pregnancy. All of the pregnant rats studied delivered in a 23 degrees C environment in spite of blood pressure control by a pressor or antihypertensive drug. At 33 degrees C, the pregnant rats were divided into two groups whose blood pressure was increased severely (160-175 mm Hg) or moderately (145-155 mm Hg) at 10 days of pregnancy. Those in the former group delivered, but those in the latter died in the final stage of pregnancy. When the pregnant rats in the group with high blood pressure on day 10 were treated with a antihypertensive drug in the middle stage of pregnancy or with a pressor drug in the final stage, the mortality rate was 100 per cent in both cases. The delivery rate was 57 per cent when the pregnant rats were treated with a antihypertensive drug from the middle to the final stage of pregnancy. In the group with low blood pressure on day 10, all of the pregnant rats delivered when they were treated with a pressor drug in the middle stage of pregnancy. However, the delivery rate was 89 per cent when the pregnant rats were treated with antihypertensive drug in the final stage of pregnancy.