TISSUE CHANGES. 417 



ef the ood i. e., the proportion of each group of food stuff 

 present in the diet has an important influence on the quantity 

 required to establish the equilibrium, or that best suited to cause 

 increase of weight or to fatten. 



It will be convenient to consider the following different cases 

 in succession : 



1. No income, except oxygen, L e., starvation. 



2. An income only equal to the expenditure found during 

 starvation. 



3. Perfect establishment of nutritive equilibrium. 



4. Excessive consumption. 



TISSUE CHANGES. 



As is well known, a deprivation of oxygen by the respiratory 

 function being stopped almost immediately puts an end to the 

 tissue changes necessary for life, so that the oxygen income can- 

 not be interfered with without instant death ensuing. Moreover, 

 it has been found that a small supply of water makes the inves- 

 tigation of the various tissue changes more reliable, by facilita- 

 ting them and prolonging life. We, therefore, commonly speak 

 of a total abstinence from solids as starvation. 



When deprived of food, those tissues upon whose activity life 

 depends must feed upon the materials stored up in some part of 

 the system. The first questions to discuss are how much the body 

 loses daily in weight during the time that it is thus feeding on 

 itself, and how far the different individual tissues contribute to 

 this loss. 



The general loss of weight is directly estimated by weighing the 

 animal, and the loss of the individual tissues is calculated by a 

 careful analysis of the various excreta, by which the exact amount 

 of nitrogen, carbonic acid, etc., are ascertained : the nitrogen cor- 

 responds to the loss of muscle ; and the carbon (after excluding 

 that portion which is the outcome of muscle change, which may 

 be calculated from the nitrogen) corresponds to the fats oxidized. 



It has been found that a starving animal loses weight at first 

 rapidly, and subsequently more slowly ; and the reason for this 

 difference is that during the first three or four days the benefit of 



