590 THE ANIMAL BODY AS A MACHINE 



We must still admit that the ratio of basal metabolism to surface, 

 although variable, is much less variable than the ratio of metabolism 

 to weight, length, temperature, or any other dimension or characteristic 

 of the individual. The possibility has not been sufficiently considered, 

 however, that many details of structural proportion in the body may 

 be correlated with superficial area rather than with weight, and that 

 the observed relationship of metabolism to surface may be thus only 

 an indirect one, representing a relationship of metabolism to a group of 

 structural elements which vary as the two-thirds exponent of the 

 body-weight or volume. Thus Dreyer has shown that the blood- 

 volume and the sectional areas of the aorta and the trachea of animals 

 of different size are proportional to W*, that is, to the surface. Frieden- 

 thal has pointed out that the sum of the non-protoplasmic materials 

 (reserve-materials, skeletal constituents and fibrous tissues) in the 

 animal body increases more rapidly with total size than the proto- 

 plasmic tissues. This is, in fact, inevitable, for the need of binding and 

 supporting tissues increases in proportion to the strains to which the 

 body is subject and these increase not only in proportion to the mass 

 but to the mass X linear dimensions of the body. A small mass of 

 protoplasm requires no binding tissues to support it, but a large mass 

 of cells would collapse of their own weight without binding, cementing 

 and supporting tissues, and the greater the distance of any mass of 

 protoplasm from the center of gravity of the whole, the greater in that 

 proportion will be its tendency to break away. Friedenthal concludes, 

 in fact, that the protoplasmic or Parenchymatous Tissues only increase 

 in proportion to the two-thirds exponent of the total weight, i.e., in 

 proportion to the surface. Since these are the tissues of highest 

 metabolic rate, their mass, together with the proportion of Endogenous 

 Catalyzers which they contain, might be expected to play a leading part 

 in determining the rate of basal metabolism. 



THE NUTRITION OF CHILDREN. 



During the early period of post-natal -development the sole normal 

 source of food among the mammalia is Milk. The milk of different 

 species of animals, however, is very far from being of constant composi- 

 tion, and we may infer that the optimal admixture of foodstuffs for 

 sucklings varies greatly with the species. The following table repre- 

 sents the composition of milk of several species, determined by Abder- 

 halden. 



One hundred parts by weight of milk contain : 



Species. Casein. Albumin. Total protein. Fat. Sugar. 



Dog 4.8 2.6 7.4 11.6 3.2 



Pig 3.8 1.5 5.2 9.5 3.3 



Sheep 4.1 0.8 4.9 9.3 5.1 



Goat 2.9 0.8 3.7 4.3 3.6 



Guinea-pig ...4.8 0.6 5.4 7.0 2.0 



Cow 2.9 0.5 3.4 3.7 5.0 



Horse 1.3 0.8 2.1 1.1 5.9 



Ass 0.8 1.1 1.9 1.4 6.2 



Human . . . . 0.8 1.2 2.0 3.7 6.4 



