(1) Comfort and health can readily be maintained in dry heat where for long periods the air temperature is above that of the body.

(2) The amount of water absolutely required, and actually consumed, is very large; and this is accounted for by the necessity for neutralising, in some circumstances, the whole heat of metabolism (requiring up to 6,000 c.c.) and in addition a variable but sometimes very large amount of heat added to the body by radiation and conduction.

(3) A healthy man carries in his body a large reserve of water, this reserve being mainly stored in muscle and being so readily available that the percentage of water in the blood is not appreciably diminished even when several litres of water have been lost by sweating. If, however, it be extensively drawn on, replacement seems to occupy many hours, and this delay is an important factor, forming a strong argument against any undue or needless use of the stored water owing to restriction of drinking.