CHAP, v.] NUTRITION. 813 



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 production, so as to 

 secure the same constant bodily temperature (and as we have just 

 seen the bodily temperature of warm-blooded animals is remark- 

 ably 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 shew 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 production of heat ; and not only is this 

 view confirmed by common experience and by our own sensations, 

 but direct calorimetric observations afford experimental 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 

 6th to the 9th 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. 

 Thus in some experiments the production at the 9th hour, after an 

 ordinary meal of meat and fat, was at a rate about 20 or 25 p.c. 

 greater than that at which it was going on before food was given, 

 and to which it subsequently sank before food was again given. It 

 would appear that if sugar be added to the meal the rise becomes 

 more marked at an earlier period, as if the economy found sugar 

 easier to consume than fat. This however is a matter which as 

 yet requires to be more fully worked out. 



Labour, muscular work, has a powerful influence in increasing 

 the production 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 even 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, 

 87, 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 labour probably 

 varies in a corresponding way. The details of this relation have 



