MECHANISM OF THE PRODUCTION OF HEAT. 453 



trated in the effects of operations upon the vaso-motor nerves and in the phe- 

 nomena of inflammation. 



Nutrition and disassimilation involve the appropriation of matters taken 

 into the body and the production and discharge of effete substances. In its 

 widest signification, this includes the consumption of oxygen and the elimina- 

 tion of carbon dioxide ; and consequently, respiration may be regarded as a 

 nutritive act. All of the nutritive processes go on together, and they all 

 involve, in most warm-blooded animals at least, a nearly uniform tempera- 

 ture. During the first periods of intrauterine life, the heat derived from the 

 mother is undoubtedly necessary to the development of tissue by a change 

 of substance, analogous to nutrition and even superior to it in activity. Dur- 

 ing adult life, animal heat and the nutritive force are co-existent. It now 

 becomes an important question to determine whether there be any class of 

 nutritive matters specially concerned in calorification or any nutritive acts- 

 exclusively or specially directed to the maintenance of the normal tempera- 

 ture of the body. 



It is evident that in normal nutrition by food, the heat of the body must 

 be maintained by changes which take place, either directly in the blood or 

 indirectly in the tissues, in alimentary matters, and that these changes involve 

 oxidation to a very considerable extent. Under ordinary conditions of nutri- 

 tion, it is assumed that the food furnishes all the material for maintaining 

 the heat of the body and for the development of force in work, such as the 

 muscular work of respiration and circulation and general muscular effort. 

 If no food be taken for a certain time, the heat of the body must be main- 

 tained, the work must be accomplished at the expense of the substance of 

 the body itself, and the individual loses weight. In order to maintain the 

 equilibrium of the body, therefore, food should be taken in quantity sufficient 

 to supply, by its changes in oxidation etc., the heat and force required. In 

 this condition of equilibrium, the body neither gains nor loses weight. To- 

 furnish a positive scientific basis for calculations with reference to these 

 points, physiologists have burned various articles of food in oxygen, and 

 have estimated their heat-value in heat-units. 



In 1866, Frankland made a number of calculations of the heat-units and 

 the estimated force-value of various articles of food, which are now accepted 

 and used by most writers upon subjects connected with the theories of ani- 

 mal heat and the source of muscular power. As regards the heat produced 

 by the oxidation of these substances in the body, if it be assumed that the 

 same quantity of heat is produced by the oxidation, under all circumstances,. 

 of a definite quantity of oxidizable matter, it is necessary simply to deduct 

 from the heat- value of articles of food the heat- value remaining in certain 

 parts of the food which pass out of the body in an unoxidized state. It was 

 in this way that Frankland arrived at a determination of the heat- value of 

 articles of food oxidized in the body. 



The following selections from Frankland's table will give an idea of the 

 heat- value of different articles of food oxidized in the body. In this table 

 the heat-units are calculated as pound-degrees. 



