ANIMAL HEAT. 519 



processes involved in the waste being the same as during a period of abstinence from 

 food. As regards the oxidation of hydrogen, we may suppose that the hydrogen of the 

 non-nitrogenized parts is used, and that the matter thus consumed is supplied again to the 

 tissues in order to maintain the physiological status of the organism. 



The supposition that water may be actually formed within the organism under certain 

 conditions not only completes the oxidation-theory of the production of animal heat, but 

 it enables us to understand certain physiological phenomena that have heretofore been 

 obscure. It is well known, for example, 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 containing a relatively small proportion of fat and liquids, and regular 

 muscular exercise attended with profuse sweating. We have seen that muscular work 

 increases the elimination of water, while it also exaggerates for the time the calorific 

 processes. The muscular exercise undoubtedly favors the consumption of the non-nitro- 

 genized parts of the body, and a diminution of the supply of hydro-carbons, carbo-hydrates, 

 and water in the food prevents, to a certain extent, the new formation of fat. By taking 

 an unnecessary quantity of liquids, we do not increase the calorific processes or promote 

 activity of the circulation, and the excess of water is usually discharged by the kidneys. 

 When, however, we exert the muscular system excessively, we increase the production of 

 water 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 increased, 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. 



We shall restrict the conclusions to be drawn from the experiments just described to 

 points connected with the production of animal heat. It is undoubtedly true that, com- 

 puting all of the force produced in the body as heat-units, more heat is generated than 

 is absolutely necessary to maintain the normal animal temperature, and that a certain 

 amount of this excess is manifested as force used in the work of respiration and circula- 

 tion and general muscular effort. The computation of the force thus used is always made 

 in accordance with the formula that one heat-unit is equivalent to 772 foot-pounds. The 

 reduction of the force of the heart and the force exerted by the respiratory muscles to 

 units of foot-pounds is so excessively difficult and uncertain that the estimates given by 

 writers ar, in our opinion, almost worthless. The same remark applies to the reduction 

 of ordinary muscular work to definite units. Without some such method of reduction, 

 however, the force exerted by muscles cannot be expressed in definite quantities. All 

 that we can do is to show, if possible, that more heat-units are produced in the body 

 than are required to maintain the heat of the body, and that a part of the excess is con- 

 verted into force. We do not conceive that the simple experiment, which shows that 

 one pound in falling 772 feet will produce heat enough to raise the temperature of one 

 pound of water one degree Fahrenheit, proves absolutely that one heat-unit produced 

 by burning food in oxygen, when the same food is oxidized in the body, making allow- 

 ance for that which escapes such oxidation, can be converted into muscular force equal 

 to 772 foot-pounds. From our own experiments upon the subject under consideration, 

 we may legitimately draw, however, the following conclusions: 



1. It is probable that nearly all the animal heat is produced by oxidation, in the 

 body, of certain elements, which are chiefly nitrogen, carbon, and hydrogen. 



2. It is probable that this oxidation takes place chiefly in the substance of the various 

 tissues, and that it is connected with the general processes of nutrition and disassimila- 

 tion. Heat is thus generated, and the final products of the chemical actions involved are 

 mainly urea, carbonic acid, and water. It must be remembered, however, that the 

 oxidation is not necessarily a process identical with combustion out of the body, but 

 that it is probably connected with a series of intricate molecular changes, which 



