I9O NUTRITION, DIETETICS AND ANIMAL HEAT 



respiratory activity increases heat dissipation for reasons al- 

 ready given. When the external temperature is high and 

 the air is dry evaporation is more abundant, and conse- 

 quently heat dissipation is greater than when the air is al- 

 ready impregnated with moisture. Hence the oppressiveness 

 of the high external temperature with high humidity. In 

 fever heat dissipation is usually increased, but to a less de- 

 gree than the production. 



Thermotaxis. Thermo taxis is the regulation of heat 

 production and heat dissipation so that the temperature of 

 the body may remain the same. It is evident that there is 

 frequently a transient increase or decrease of thermogen- 

 etic activity ; unless there be a corresponding change in ther- 

 molytic activity the temperature will be disturbed. 



The temperature of the body is not necessarily raised 

 when heat production is increased, or lowered when it is de- 

 creased ; for heat loss may be, and in health is, correspond- 

 ingly increased or diminished. Conversely, a change in heat 

 loss does not necessarily mean an opposite change in the 

 body temperature. Alterations which do occur in the tem- 

 perature are the result of the improper regulation of the 

 heat at hand. For instance, fever may result from average 

 heat production and deficient heat loss ; from increased heat 

 production and heat loss when the latter is increased less than 

 the former; from diminished heat production and heat loss 

 when the latter is diminished less than the former, etc. A 

 subnormal temperature is caused by opposite conditions. 

 The temperature remains constant when heat production and 

 loss are normal, or when they are increased or decreased 

 correspondingly. 



Thermotactic activity is the result of changes in the tem- 

 perature of the blood, or of cutaneous impressions. A rise 

 in the temperature of the blood excites heat loss, as indi- 

 cated. A cold atmosphere increases heat loss, but at the 

 same time it makes impressions on the cutaneous nerves 

 which, when carried to the centers, excite heat production 



