ANIMAL HEAT UNDER LA1JOUR. 533 



mineral matter increased by a third of the original quantity, 

 thus 



251 - 150 101 ! Difference between diet at rest and diet 



( under exertion, heat-givers. 

 59 - 28.9- 30.1 do., flesh-formers. 

 19.4 13 = 6.4 do., mineral matter. 



It is usual to describe the function of animal heat as a pro- 

 vision to maintain the system at a standard temperature in a 

 medium, like the earth's atmosphere, almost uniformly colder 

 than itself ; but under severe bodily exertion much more heat 

 is generated than is sufficient for this purpose, so that there is 

 a superfluity of heat thrown off, apparently without serving 

 any useful end. This is an important subject for speculation, 

 but of too great magnitude to be entered upon here. For 

 example, it does not clearly appear that in augmenting the 

 daily diet of the horse from that sufficient for the state of rest 

 to that requisite for the state of labour, it is absolutely neces- 

 sary to increase the amount of heat and fat giving principles, 

 as well as tliat of the flesh-forming principles. This, it must 

 be confessed, is at present merely a speculative question, because 

 we can hardly increase the amount of the flesh-formers with- 

 out necessarily increasing that of the heat and fat giving, since 

 both are usually bound up together in one article of food. 

 Nevertheless, speculative as it is, it is desirable it should be 

 investigated and settled as opportunities offer. Some facts 

 have been ascertained bearing on this subject. Thus, Beclard 

 found that the heat developed in a muscle is in inverse ratio 

 to the mechanical effects produced, as, in trying to raise 

 insuperable weights, more heat is evolved than in lifting 

 lighter weights ; and Hern has shown, by direct experiment on 

 a treadmill, that less heat is evolved for each gram of oxygen 

 taken into the body when hard work is done outside the body.* 

 * See Playfair, Lecture, p. 38. 



