1 88 NUTRITION, DIETETICS AND ANIMAL HEAT 



Thermogenesis. Thermogenesis, or the production of heat, 

 is the result of activity on the part of tissues, nerves and centers. 

 Now, the potential energy of the food stuffs is the ultimate 

 source of all bodily heat no matter how it may be manifested, 

 and it is evident from what has been said already that all the 

 tissues of the body are heat-producing tissues, because oxidation 

 processes go on in them all. But muscular tissue seems to be 

 endowed with special heat-producing 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 accord- 

 ance with the needs of the economy by means of a nervous mech- 

 anism, making the production of heat analogous to secretion. 

 Separation of a muscle from its nerve does not stop thermogenesis, 

 but markedly interfers 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. Cen- 

 ters increasing thermogenesis are probably in the caudate nuclei 

 of the corpora striata, the optic thai ami, pons and medulla. 

 Irritation of these regions causes a rise in temperature. The 

 location of the thermo-inhibitory centers is a matter of specu- 

 lation. The general thermogenic centers in the cord probably 

 maintain a fairly constant production of heat independently, 

 but they are subservient to encephalic centers which excite 

 them to increased or decreased activity by reason of certain 

 impressions, cutaneous or otherwise, which they have received. 



Heat Loss. About 85 per cent, of animal heat, discharged 

 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 



