696 



ANIMAL HEAT 



equilibrium is maintained. There is reason to believe that at a 

 temperature equal to that of the human body, the heat-production 

 of a frog per unit of mass would equal that of a man or other large 

 mammal, although it would be far less than that of a small homoio- 

 thermal animal. This is in favour of the view that in the larger 

 mammals a nervous regulation of the intensity of the metabolism 

 is not of prime importance. 



Relations between Heat-Production, Surface Area, and Blood-Flow. 



The following table shows how close is the agreement in the heat- 

 production per unit of surface for animals of different species and very 

 different body- weight: 



The relation between heat-production and surface area has been rein- 

 vestigated by modern methods. Some observers, notably Benedict, 

 are inclined to deny that any simple proportion exists between the 

 basal metabolism and the area of the skin. They consider that the 

 magnitude of the metabolism is related rather to the mass of active 

 protoplasm, which is a different quantity from the weight of the body, 

 the fatty tissues e.g., contributing largely to the body-weight, but 

 little to the metabolism. On the other hand, Lusk. Du Bois, and their 

 fellow-workers, believe that when the surface area is accurately cal- 

 culated there is no reason to doubt the hitherto accepted view of a 

 proportionality between heat-production and area of surface. It must 

 be remembered that it is only for subjects in the same general physio- 

 logical state that the proportionality is supposed to hold. Nobody 

 imagines, for instance, that a patient with exophthalmic goitre will 

 have the same heat-production per unit of surface as a normal indi- 

 vidual. Nor can an infant be expected to be exactly comparable with 

 an adult, since it differs so much not only in the proportions of the 

 body and the relative size of the various organs, but also in its meta- 

 bolism. It has been found, as a matter of fact, that the heat-produc- 



cumference or width of each of the characteristic parts of the body. Con- 

 stants have been worked out for each part by comparison of the actual area 

 of a mould applied to the skin with the data obtained by the measurements. 

 This so-called ' linear formula ' does not involve the body- weight, and gives 

 good results with bodies of very different size and shape (Du Bois). Bene- 

 dict has also developed a photographic method of obtaining the surface area. 

 The main interest of such measurements lies in their bearing upon the relation 

 between the metabolism and the body-surface. 



