RESPIRATORY EXCHANGE OF ANIMALS AND MAN 



certain organs by the researches of Dreyer and his collaborators [1912] 

 who found that the blood volume, the sectional area of the aorta and of 

 the trachea of animals of different size, are proportional to W s , that is 

 to the surface. 1 For such organs as the lungs or kidneys which are 

 built up of elementary units (alveoli, Malpighian bodies) the total 

 active surface would be proportional to the body surface if the 

 number of elements were always the same and their linear dimen- 

 sions proportional to those of the body. This is far from being the 

 case however. 



The arguments so far mentioned, Rubner's as well as Hoesslin's, 

 are of a more or less teleological character, and do not consider the 

 mechanism by which the metabolism must be supposed to be regul- 

 ated. Hoesslin alone has touched upon this point. He assumes 

 that the metabolism of a tissue depends upon and is proportional to 

 the supply of oxygen, an assumption which, as shown on page 78, 

 may be true with regard to the muscles. According to Hoesslin the 

 circulation rate per unit weight and consequently the supply of oxy- 

 gen must for anatomical reasons be proportional to W^ (the body 

 surface), and the regulation of the metabolism in accordance with the 

 experimental results obtained on warm-blooded animals would follow 

 from these premises. 



Hoesslin's argumentation is certainly inconclusive though he has 

 given much thought to the problem, which appears to the writer as 

 being so important that it would well deserve a renewed treatment 

 both experimental, as far as cold-blooded animals are concerned, and 

 theoretical. Hoesslin has been careful to point out that if his deduc- 

 tions are correct they must apply with equal force to cold-blooded 

 animals. It is obvious that measurements of the actual body surface 

 or the use of elaborate formulas to obtain the surface from certain 

 linear measurements can have a real significance only when Rubner's 

 view of the conditions for loss of heat as the factor directly governing 

 the metabolism is accepted In the opinion of the writer the reasons 

 against Rubner's view are very strong, and the line of inquiry initiated 

 by Dreyer is much more likely ultimately to clear up the relationship 

 between size and metabolism. The metabolism should not therefore 

 be expressed per sq. m. or any other unit of surface but as a function 

 of W". For warm-blooded animals n can be taken, at least provision- 

 ally as . 



1 In the cold-blooded frogs and lizards, no proportionality exists between body surface 

 and blood volume, which increases with the size even more rapidly than the weight, being 

 proportional to W 1 ' 2 , as shown by Fry [1913]. 



