ANIMAL HEAT. 515 



this view, physiologists have burned various articles of food in oxygen and have calcu- 

 lated their heat- value. This has heen expressed in what are called heat-units, the Eng- 

 lish value of a heat-unit heing the amount of heat required to raise one pound of water 

 one degree Fahrenheit. It is also calculated that one heat-unit converted into force 

 will raise 772 pounds one foot high, or is equal to 772 foot-pounds. The theory of the 

 heat-value and the force-value of food, based upon these premises, is the following: 



The heat-value of food may be expressed in a definite number of heat-units. A cer- 

 tain proportion of these heat-units serves to maintain the standard animal temperature. 

 A certain proportion is converted into the force used in the muscular work of respira- 

 tion and circulation. A certain proportion is used in ordinary muscular work. If the 

 supply of food be in excess of these various requirements, a certain part of it is not used 

 and the body may gain in weight. If the supply of food, however, be below the de- 

 mands of the system, a part of the tissues of the body itself is consumed, and there 

 must be a loss of weight. 



Following the observations made by Fick and Wislicenus, in 1866, by which these 

 observers attempted to show that nearly all the force resulting from muscular action is 

 due to the oxidation of non-nitrogenized matters, physiologists have estimated the heat- 

 value and the force-value of different articles of food. They have reasoned that the 

 food, by its oxidation in the body, is capable of producing a certain amount of heat and 

 that a part of this heat is converted into force. A method now employed to calculate 

 the heat produced is to subtract the daily mechanical force expended from the total 

 force-value of the food, the result giving the daily formation of heat. Foster estimates 

 in this way that " between one-fifth and one-sixth of the total income is expended as 

 muscular labor, the remaining four-fifths or five-sixths leaving the body in the form of 

 heat." The reduction of heat-units to units of force is made in accordance with Joule's 

 formula, already referred to, that one heat-unit is equal to 772 foot-pounds, or will raise 

 772 pounds one foot high. - 



In 1860, Franldand 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 animal 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 amount 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 Frank- 

 land arrived at a determination of the heat-value of articles of food oxidized in the body. 

 As we have already stated, according to the observations of Senator and of Draper, the 

 actual heat produced by the body is equal to about four heat-units per pound weight 

 per hour. We shall assume that this estimate, as well as the determinations made by 

 Frankland of the heat-value of certain articles of food, are reasonably accurate, and we 

 shall treat them as definite propositions in discussing the following observations : 



Observation 1. In 1870, we had occasion to note the work, the quantity of food 

 taken, and various other conditions in a healthy man for several consecutive days. The 

 observations were made at that time with another object in view, but the data obtained 

 will serve in the present argument. "We shall here make use of the estimates made for 

 five consecutive days, during which the subject of the observations walked 317^ miles. 

 In these calculations, we estimate the heat-value of the loss of weight of the body ao 

 well as that of the food. The nkrogenizsd food and loss of body-weight gave 13,416-64 

 heat-units, and tho non-nitrogenized food, 19,521-41 heat-units, making a total of 32,- 

 938-05. The heat actually produced by the body, at four heat-units per pound per hour, 

 was estimated at 55,440-00 heat-units. This leaves 22,501 '25 heat-units not accounted 

 for, or about fort: P er cent., not taking into consideration the heat-units converted into 

 force expended in circulation and respiration and in walking 317i miles. 



