IXFLUENC'E OF COOLING POWERS OF ATMOSPUERE. 



287 



but aiiso of niuseular tissue." I'or isome time after an adult indi- 

 vidual lias settled at one of these high altitudes the nitrogen 

 output is less tha,n the nitrogen intake. There is an actual 

 building up of new museuhir tissue. 



The profound influence of the cooling power of the atmosphere 

 on the metabolism has been abundantly demonstrated.* Leonard 

 Hill has provided us with an instiTiment, the kata thermometer, 

 1)}' means of which the cooling power of the atmosphere can be 

 leadil}' determined. It is found that for active metabolism to take 

 place in mammals, a moderately high cooling, power of the atmos- 

 phere is desirable. In some mammals the response to very high 

 cooling powere is by a partial arrest of metabolic activities as 

 occui-s in hibernating animals in winter, when there is a pro- 

 longed period of high cooling powers. This habit is evidently to 

 be explained as an adaptation to the lessened food supply in 

 w inter rather than a,s a direct reaction to a high cooling power. 

 If the animal, in the hibernating condition, be submitted to 

 extreme conditions of cold, its metabolic activities increase and 

 the animal wakes ujd ; thus death from freezing is prevented. 



Observations made on guinea pigs last summer in Johannes- 

 burg revealed the fact that the animals invariably ate more during 

 the cool spells of weather than during the more usual hot sj^ells. 

 This is shown in Table I. During the first ten days of Febiiiary 



TABLE I. 



Amovmt of Food Eaten by a Guinea-Pig during Cool and Hot 

 Periods in Summer. 



♦Millicalories per sq. cm. per second. 



The Kata readings were taken in the Animal Room at 12 a.m. each day. The 

 weight of the animal was 520 gms. on Feb. 1 and on Feb. 24. During that 

 period it did not rise above 525 gm. or fall below 500 gm. 



