THE ENERGY OF THE BODY. 501 



be called its specific coefficient, and every individual his personal coefficient 

 of heat-production, the coefficient being the expression of the inborn qualities 

 proper to the living substance of the species and of the individual. 



A larger living body will naturally produce more heat than a smaller 

 living body of the same nature, since the larger body possesses, so to speak, 

 a greater number of heat-producing units. But this is neutralized by an 

 opposing tendency. The smaller body, having relatively to its bulk a 

 larger amount of surface, loses heat at a more rapid rate than does the 

 larger body ; and, therefore, to maintain the balance between loss and pro- 

 duction, so" as to secure the same constant bodily temperature (and, as we 

 have just seen, the bodily temperature of warm-blooded animals is remarka- 

 bly uniform), it must produce heat, per unit of its body, at a more rapid 

 rate. As a rule, the greater loss of heat owing to the relatively greater 

 .surface is so marked that of two animals having the same constant bodily 

 temperature, of two species of mammals, or of two individuals of the same 

 race, we should expect the smaller one to produce a relatively larger amount 

 of heat. And direct calorimetric observations show that this is so. The 

 struggle for existence has raised what we have just called the specific or 

 personal coefficient of the smaller animal. 



From what we have seen concerning the immediate effects of a meal, we 

 should be inclined to expect that food would temporarily increase the pro- 

 duction of heat ; and not only is this view confirmed by common experience 

 and by our own sensations, but direct calorimetric observations afford ex- 

 perimental proof of its truth. In the dog it has been found that the rate of 

 production increases after a meal, reaching its maximum from the sixth to 

 the ninth hour, and then declining to a level which may be regarded as that 

 secured by the general metabolism of the body, and which appears to be 

 maintained with remarkable constancy until after long starvation the 

 economy begins to break down. 



Labor, muscular work, has a powerful influence in increasing the pro- 

 duction of heat. As we have seen, of the total heat produced in the body, 

 a certain portion must always be attributed to muscular contractions, which 

 ^ven in the most quiet body are always going on ; in an ordinary active 

 body a considerable quantity of heat must be thus generated. Hence, the 

 more active the body the greater the production of heat. As we stated 

 before ( 85), in a contraction the proportion of the energy set free to do 

 work to that set free as heat appears to vary under different circumstances ; 

 and the increase of heat due to labor probably varies in a corresponding 

 way. The details of this relation have yet to be worked out, but we may at 

 least conclude that, when a man pushes his daily labor beyond the 150,000 

 kilogramme-metres, the additional energy thus leaving his body as work done 

 is not taken out of the 850,000 kilogramme-metres given in 442 as the 

 average daily output of heat, but the total setting free of energy and the 

 total production of heat is at the same time increased. And it need hardly 

 be said that the figures in question give only an average estimate for a man 

 of average build and weight, taking an average amount of average food, 

 and doing an average amount of work. 



448. The production of heat thus determined by these several influ- 

 ences, some of which are themselves regulated by the nervous system, is 

 further regulated in a remarkable manner. For it is not solely by variations 

 in the loss of heat that the constant temperature of the warm-blooded animal 

 is maintained. Variations in the amount of heat actually generated in the 

 body constitute an important factor, not only in the maintenance of the 

 normal temperature, but also in the production of the abnormally high or 

 low temperatures of various diseases. Many considerations have long led 



