456 NUTRITION ANIMAL HEAT AND FORCE. 



oxidation of hydrogen in this formation of water, it is probable that the 

 hydrogen of the tissues is used and that the matter thus consumed is sup- 

 plied again to the tissues in order to maintain the physiological status of the 

 organism. Adding the heat- value of the water thus produced to the heat- 

 value of food, there is little difficulty in accounting for the heat and force 

 actually produced and expended. 



The demonstration that water is actually formed within the organism, 

 under certain conditions, not only completes the oxidation-theory of the pro- 

 duction of animal heat, but it affords an explanation of certain physiological 

 phenomena that have been heretofore obscure. It is well known, for exam- 

 ple, that a proper system of physical training will reduce the fat of the body 

 to a minimum consistent with health and strength. This involves a diet con- 

 taining a relatively small proportion of fat and liquids, and regular muscular 

 exercise attended with profuse sweating. Muscular work increases the elimi- 

 nation of water, while it also exaggerates for the time the calorific processes. 

 Muscular exercise undoubtedly favors the consumption of the non-nitrogenized 

 parts of the body, and a diminution of the supply of fats, carbohydrates and 

 water in the food prevents, to a certain extent, the new formation of fat. In 

 excessive muscular exertion, the production of water is increased and the 

 circulation becomes more active. The volume of blood then circulating in 

 the skin and passing through the lungs in a given time is relatively in- 

 creased, and there is an increased discharge of water from these surfaces* 

 The same condition that produces an increased quantity of water in the 

 body and has a tendency to exaggerate the process of calorification seems to 

 produce also an increased evaporation from the surface, which serves to 

 equalize the animal temperature. 



Equalization of the Animal Temperature. A study of the phenomena of 

 calorification in the human subject has shown that under all conditions of 

 climate the general heat of the body is equalized. There is always more or 

 less loss of heat by evaporation from the general surface, and when the sur- 

 rounding atmosphere is very cold, it becomes desirable to reduce this loss to 

 the minimum. This is done by appropriate clothing, which must certainly be 

 regarded as a physiological necessity. Clothing protects from excessive heat 

 as well as from cold. Thin, porous articles moderate the heat of the sun,, 

 equalize evaporation and afford great protection in hot climates. In excessive 

 cold, clothing moderates the loss of heat from the surface. When the body 

 is not exposed to currents of air, garments are useful chiefly as non-conduct- 

 ors, imprisoning many layers of air, which are warmed by contact with the 

 person. It is also important to protect the body from the wind, which greatly 

 increases the loss of heat by evaporation. 



When from any cause there is a tendency to undue elevation of the heat 

 of the body, cutaneous transpiration is increased, and the temperature is kept 

 at the proper standard. This has already been considered in treating of 

 the action of the skin, and facts were noted showing that men can work 

 when exposed to a heat much higher than that of the body itself. The 

 quantity of vapor that is lost under these conditions is sometimes very large 



