l88 NUTRITION, DIETETICS AND ANIMAL HEAT 



the ultimate source of all bodily heat no matter how it may 

 be manifested, and it is evident from what has been said al- 

 ready that all the tissues of the body are heat-producing tis- 

 sues, because oxidation processes go on in them all. But 

 muscular tissue seems to be endowed with special heat-pro- 

 ducing capabilities, so much so that it is said to generate 

 heat as a specific product, and not as a mere incident of its 

 metabolism. Muscle will reproduce heat when entirely at 

 rest when the nutritive metabolic changes are practically 

 nothing. The process seems to be regulated in accordance 

 with the needs of the economy by means of a nervous me- 

 chanism, making the production of heat analogous to secre- 

 tion. Separation of a muscle from its nerve does not stop 

 thermogenesis, but markedly interferes with it in that part. 

 The existence of distinct thermogenic nerves has not been 

 demonstrated. The existence of specific thermogenic centers 

 seems certain. Some of them increase and some decrease 

 thermogenesis. 



The general thermogenic centers are in the spinal cord. 

 Centers increasing thermogenesis are probably in the cau- 

 date nuclei of the corpora stria, the optic thalami, pons and 

 medulla. Irritation of these regions causes a rise in temper- 

 ature. The location of the thermo-inhibitory centers is a 

 matter of speculation. The general thermogenic centers in 

 the cord probably maintain a fairly constant pro- 

 duction of heat independently, but they are subservient to 

 encephalic centers which excite them to increased or de- 

 creased activity by reason of certain impressions, cutaneous 

 or otherwise, which they have received. 



Heat Loss. About 85 per cent, of animal heat, dis- 

 charged as such, is lost by radiation and evaporation from 

 the skin; about 12 per cent, is dissipated in the lungs by 

 evaporation and in warming the inspired air ; the remainder 

 is discharged in the urine and feces (disregarding the small 

 amount which goes to warm ingested articles). 



Hbat is radiated from the body just as from a hot stove. 



