THE STATISTICS OF NUTRITION. 483 



method is, however, open to us the statistical method. We may ascertain 

 the total income and the total expenditure of the body during a given 

 period, and by comparing the two maybe able to draw conclusions concern- 

 ing the changes which must have taken place in the body while the income 

 was being converted into the output. Many researches have been carried 

 out by this method ; but valuable as are the results which have been thereby 

 gained, they must be received with caution, since in this method of inquiry 

 a small error in the data may, in the process of calculation and inference, 

 lead to wrong conclusions. The great use of such inquiries is to suggest 

 ideas, but the views to which they give rise need to be verified in other 

 ways before they can acquire real worth. 



Composition of the animal body. The first datum we require is a know- 

 ledge of the composition of the body, as far as the relative proportion of the 

 various tissues is concerned. In the human body the proportions by weight 

 of the chief tissues, in the fresh state, are probably somewhat as follows : 



Adult man. Newborn baby. 



Per cent. Per cent. 



Skeleton 15.9 17.7 



Muscles 41.8 22.9 



Thoracic viscera 1.7 3.0 



Abdominal viscera 7.2 11.5 



Fat 18.2] 900 



Skin 6.9] 



Brain 1.9 15.8 



An analysis of a cat has given the following result : 



Per cent. 



Muscles and tendons , 45.0 



Bones 14.7 



Skin . 12.0 



Mesentery and adipose tissue 3.8 



Liver 4.8 



Blood (escaping at death) 6.0 



Other organs and tissues 13.7 



One point of importance to be noticed in these analyses is that the 

 skeletal muscles form nearly half the body ; we have already seen ( 38) 

 that about a quarter of the total blood in the body is contained in them, and 

 have already ( 398) insisted that a large part of the metabolism of the 

 body is carried on in the muscles. Next to the muscles we must place the 

 liver, for though far less in bulk than them, it is subject to a very active 

 metabolism ; this is suggested by the fact that it alone may hold about a 

 quarter of the whole blood, and is also indicated by the numerous facts 

 brought before us in the preceding chapter. 



434. The starving body. Before attempting to study the influence of 

 food, it will be useful to ascertain what changes occur in the body when all 

 food is withheld. A cat of known weight was starved for thirteen days. 

 At the beginning of the period the body was presumed to have the compo- 

 sition above given ; at the close of the period a direct analysis of the body 

 was made. From this it appeared that during the hunger period the cat 

 hand lost 734 grammes of solid material, of which 248.8 were fat and 118.2 

 muscle, the remainder being derived from the other tissues. The percent- 

 ages of dry solid matter lost by the more important tissues during the period 

 ivere as follows : 



