416 



MANUAL OF PHYSIOLOGY. 



gen passes off with the urine, and about nine-tenths of the carbon 

 escapes by the lungs as CO a , the remaining one-tenth passing off 

 by the intestine and kidneys. Three-fourths of the water is found 

 in the urine, and one-fourth goes off from the skin and lungs. 



The following table shows the items of the general loss, and the 

 amount per cent, which passes out by the chief channels of exit: 



As the loss of weight of an animal's body during starvation 

 is at first rapid and then more gradual, so also the amount of 

 material eliminated is found to diminish much more slowly after 

 the first few days. This is well seen from the nitrogenous elimi- 

 nation. For the first four days the fall in the amount of urea 

 excreted is very rapid; it then decreases almost constantly until 

 the death of the animal, only slightly decreasing in proportion 

 as the animal slowly decreases in weight. This has led to the 

 conclusion that the amount of nitrogenous material eliminated 

 during ordinary circumstances, with a full diet, comes partly 

 from used-up nitrogenous tissues, and partly from nitrogenous 

 materials which have never really entered into the composition of 

 the tissues, but rather are present as surplus or floating nitrogenous 

 pabulum. Hence, two kinds of proteid are supposed to exist in 

 the body, viz., (1) that forming part of the tissues, and (2) that cir- 

 culating as a ready supply for the nutritive demands of the tissues. 



In the second case mentioned, namely, where an amount of food 

 is supplied which is just equal to the expenditure which was found 

 to take place during starvation, one might suppose that the diet, 

 though minimal, would yet suffice to preserve the normal body- 

 weight. However, practice shows this to be far from what actually 

 occurs. 



An animal, fed on diet equal in quantity to the outgoings dur- 

 ing starvation, continues to lose weight, and the quantity of ui- 



