CHAP, v.] NUTRITION. 851 



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 

 yet to be worked out, but we may at least conclude that, when 

 a man pushes his daily labour beyond the 150,000 k.-m. while 

 continuing to live on the diet detailed in 527, the additional 

 energy thus leaving his body as work done is not taken out of the 

 850,000 k.-m. given in 528 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. 



534. The production of heat thus determined by these 

 several influences", some of which are themselves regulated by the 

 nervous system, is further regulated in a remarkable manner. 



