916 SPECIAL PHYSIOLOGY. 



Calorific Work of the Body. 



The number of heat-units given off by a dog in 24 hours, having 

 been ascertained to be 393,000, the number evolved, in the same time 

 by a Man weighing seven times as much as the dog, would be 2,751,- 

 000 heat-units. (Despretz.) From calculations of the number of heat- 

 units given off by the body in various ways by radiation, by evapor- 

 ation of water, and by the warming of the respired air and excreta it 

 has also been estimated that the daily loss, and therefore the daily 

 production of heat by it, amounts to 2,700,000 heat-units. (Helrnholz.) 



Comparison of the Daily Amount of the Animal Heat, with the Quantity of 

 Carbon and Hydrogen oxidized in 24 Hours. 



Now the quantity of carbon in the daily food, according to Table A, at p. 

 901, is 9.93 oz. or 281.2 grammes ; the quantity of hydrogen not already com- 

 bined with its due proportion of oxygen in the carbhydrates is 0.64 oz. or 

 18.86 grammes. Deducting from these the quantities of those elements con- 

 tained in the urine and solid excreta, Table B, viz., 1.05 oz. or 29.8 grammes 

 of carbon, and 0.2 oz. or 6.3 grammes of hydrogen, there remains a residue of 

 251.4 grammes of carbon, and of 12.56 grammes of hydrogen, free for conver- 

 sion into carbonic acid and water. The 251.4 grammes of carbon, multi- 

 plied by its heat-coefficient 8080, produce 2,031,312 heat-units ; whilst 12.56 

 grammes of hydrogen, multiplied by its heat coefficient 34,462, give 432,842 

 heat-units, the total being 2.464,154 heat-units. (Vierordt.) This calculation 

 shows a deficit in the heat, derivable from the combustion of the daily food, as 

 compared with that given off daily by the body, of about 286,800 heat-units, or 

 about y^-th only of the total estimated quantity of heat given oft* in the day. 

 It has been supposed that the heat evolved by the sulphur and phosphorus 

 oxidized in the body, would go far to meet this deficit. But in 120 grammes 

 of albumen, the supposed daily supply, there are only 1.4 grammes of sulphur ; 

 and, as the heat-coefficient of this element is 2307, the heat from that source, 

 provided all the sulphur were oxidized, which is not the case, would only 

 amount to about 32,300 heat-units ; the phosphorus would yield a somewhat 

 smaller number. Moreover, there are considerations which would appear to 

 make the deficit still worse. Thus, although the hydrogen of the starchy food 

 is excluded by Vierordt, because, being present with oxygen in the propor- 

 tions to form water, it is probably already so combined, and therefore unable 

 to evolve any further heat of combustion, yet no deduction is made for such 

 hydrogen as may be balanced by the oxygen in the fatty and albuminous food. 

 In this fat and albumen, besides the oxygen which passes out with the urea 

 and the solid excreta, sufficient exists to unite with, and so neutralize, about 2 

 grammes of hydrogen ; and if it be so combined, a loss of heat power must be 

 admitted of about 68,900 heat-units. A small quantity of the carbon and hy- 

 drogen of the food also disappears unoxidized as carburetted hydrogen. It is 

 furthermore usually maintained, that a certain quantity of chemical action is 

 transformed into external mechanical work, without being converted into heat 

 in 'the body; and this quantity has been, estimated as high as 235,000 heat- 

 units. From these circumstances, the total deficit in the heat-units of the food 

 as compared with those supposed to be given off from the body, would be 500- 

 000, i. e., between J ^th and th of the daily heat. 



This discrepancy may, however, be fully explained by possible errors in the 

 larger data. Thus, the estimated weight of the human body, and therefore 

 the number of heat-units producible by it, in proportion to the particular dog 

 experimented upon, by Despretz, may be too lar^e; or the daily supply of car- 

 bon and hydrogen in the food may be underrated for a man of the estimated 

 weight. Vierordt himself elsewhere assumes only 2,500,000 heat-units as the 

 average daily quantity evolved by an adult; and the same number has been 

 accepted by Carpenter as the probable number for a man weighing 180 Ibs., 



