A CRITIQUE OF THE BODY-SURFACE LAW. 135 



duction. Just why this should be we do not know. It reminds us at once of 

 Newton's law that the cooling of bodies is proportional to their surface-area, 

 but the metabolism does not follow this law when the external temperature 

 is raised or lowered." 



The foregoing review, while fragmentary, may give a general idea 

 of the attitude of physiologists toward the problem of body-surface 

 area in relation to metabolism. One essential distinction has not 

 always been clearly drawn by those who have written on the so-called 

 body-surface law. One may inquire whether the law holds for the 

 different species of animals which vary greatly in size, or he may 

 inquire whether it is valid when applied to individuals differing in size 

 within the same species. In brief the inter-specific and the intra-specific 

 applicability of the so-called law present two different problems. It 

 is quite conceivable that it might be very applicable intra-specifically 

 but not inter-specifically or vice versa. 



In this volume we shall limit ourselves chiefly to the question of 

 intra-specific applicability. 



2. PHYSIOLOGICAL EVIDENCE ON THE BODY-SURFACE LAW. 



Direct physiological evidence of an experimental nature of two 

 sorts are available. The first is that afforded by determinations of 

 metabolism in similar organisms subjected to different external tem- 

 perature. The second is that afforded by measures of metabolism 

 secured on individuals of like body-surface but in different physio- 

 logical state. 



The physical basis of the body-surface law has often been stated 

 to be Newton's "law of cooling." Some of the earlier physiological 

 writers seem to have fully understood the nature of Newton's law, but 

 in recent years a confused and inadequate conception of this law has 

 established itself in physiological literature. Physiologists have stated 

 the physical law as they would like it to be rather than as it really is. 



For example the immediately foregoing quotation from one of the 

 Harvey lectures 2S is quite typical of the conception of Newton's law 

 which has been held by physiologists, including the workers at the 

 Nutrition Laboratory. 



But Newton's law is not primarily a surface law at all, but a law 

 of the rate of cooling, now known to have only a limited applicability 

 even in the simpler cases of controlled physical experimentation. Heat 

 is lost by cooling bodies by convection, conduction, and radiation. The 

 relative importance of these three methods depends upon the nature 

 of the surface and the nature of the surrounding medium. In the 

 majority of cases of transference of heat all these modes are simultane- 

 ously operative in a greater or less degree, and the combined effect is 

 generally of great complexity. The different modes of transference 



2 The Harvey Lectures, 1915-1916, p. 106. 



