232 



NUTRITION 



Thermotaxis. The heat and other energy of the animal body are pro- 

 duced very largely by two sorts of processes. One of these is chemical 

 namely, metabolism (chemism), the other mechanical, friction. Besides 

 these two and the heat afforded from without by warm air, water, and 

 food, there are theoretically three other possible nutritional sources. 

 These three are the condensation of air in the lungs, the liquefaction of 

 gases, and the solidification of liquids. These produce so small an 

 amount of body heat that they may be entirely neglected. Reichert 

 estimates that of the two most important means of heating the body, 

 the chemism provides about 90 per cent, of heat, and the friction only 

 about 10 per cent. 



FIG. 126 



Higher 

 Temperature. 



Muscular Chemism. 



Glandular Chemism 



Nervous Chemism. 



Friction 



Clothing 

 Environmental Heat 



Food 

 , Vaso-constric tion 



Atropin. 



Radiation and Conduction 



Dermal Evaporation 



Respiratory Evaporation. 



Expired Air. 



Urine- 



Feces 



test 



Cold Baching 



vaso-cfiiation 



Alcohol. 



Human thermotaxis. The processes and conditions on the ileft hand make for greater heat- 

 production or heat-conservation, while those on the right exert their influences toward less heat- 

 production or for heat-loss. 



Sources of heat from movement are the circulation, the lively and 

 forcible churning of food-masses in the small intestine and by the anti- 

 peristalsis in the colon and rectum, the torsion of the costal cartilages in 

 inspiration, and the rush of air up and down the bronchi and trachea. 

 Everywhere, in short, that one bit of tissue or of liquid moves against 

 another, heat from friction is liberated, and movement, both molar and 

 molecular, is universal in the organism. All these many varied move- 

 ments combined, however, furnish to the body only a small fraction of 

 its internally derived heat (Fig. 126). 



The means by which heat and energy are lost or expended in the body 

 may be mentioned under seven heads, the most important coming first 

 in the list: Radiation and conduction from the body; evaporation of 



