414 MANUAL OF PHYSIOLOGY. 



material eliminated and stored up in the body respectively varies 

 as the income is increased; (4) and finally, that the quality of 

 the food 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, i.e., starvation. 



2. An income only equal to the expenditure found during starv- 

 ation. 



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 investi- 

 gation of the various tissue changes more reliable, by facilitating 

 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 b.vn found that a starving animal loses weight at first 



