NORMAL PROCESSES OF ENERGY METABOLISM 595 



to admit the preponderating influence of surface upon the apportionment of 

 the maintenance ration." 



This law of surface a few years later was placed upon a firmer basis 

 by researches of Rubner(o-) upon dogs and of Richet(c) upon rabbits. 



A small animal has a greater surface, in proportion to its weight, than 

 has a large animal. This will be clear from the following illustration. 

 Suppose we have two spheres of two and four centimeters diameter. The 

 surface of the smaller would be 12.56 square centimeters and of the larger 

 50.24 square centimeters. The volume of the first would be 4.18 c.c. and 

 of the latter 33.49 c.c. The surface of the smaller, in proportion to its 

 volume, therefore, would be as 3:1, while of the larger it would be only 

 as 1.5 :1. Since, now, more than four-fifths of the animal's heat escapes 

 . through the skin, by one physical means or another, it is clear that heat 

 must be produced in proportion to the surface rather than in proportion 

 to the mass, if the body temperature is to be maintained. Hence, if two 

 animals, with similar coats of fur, had skin surfaces that bore to each 

 other the relation of these spheres, the smaller animal would produce twice 

 as much heat per unit of weight as the larger. Rubner found that the 

 average heat production per square meter of body surface for man, dog, 

 rabbit, guinea pig, and mouse was 1,088 calories with variations of -j- 104 

 calories to 103 calories, i. e., of about ten per cent either way. 



a. Measurement of the Surface Area. Several methods have been 

 proposed for determining the surface area of the human subject. The first 

 was that of Meeh who marked out some parts of the body, which were 

 favorable for the purpose, in geometrical figures, covered them with trans- 

 parent paper and made tracings of the figures. The areas of these figures 

 were then calculated or determined by weighing the paper. Other parts 

 of the body were measured directly by wrapping with millimeter paper. 

 Bouchard suggested a plan which was later improved upon by DuBois and 

 DuBois (a), namely, of clothing the body in tights made of some thin in- 

 elastic material which could be weighed. D'Arsonval(e) clothed a man in 

 silk tights and after charging the clothing with electricity, determined the 

 surface relative to a metal plate of known surface by releasing the charge 

 as from a Ley den jar. Lissauer measured the surface of dead infants by 

 covering the skin with adhesive material, applying silk paper, and then 

 measuring the area of the paper by means of a planimeter. 



The measurement was accomplished by DuBois in the following man- 

 ner. A light, flexible, inelastic covering was obtained by clothing the body 

 with a close-fitting knitted union suit, and pasting this over with ad- 

 hesive paper. But instead of attempting to weigh this "model" of the 

 body surface, it was cut up into pieces which would lie out flat and the 

 area of each piece determined by photographing it on sensitive paper. 

 The total area was then found by weighing the photographic silhouettes 

 and comparing with the weight of a unit area of the same sensitive paper. 



