FOOD REQUIREMENTS. 



419 



by the intestine and kidneys. Three-fourths of the water are 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 nitro- 

 genous pabulum. Hence, two kinds of proteid are supposed to 

 exist in the body, viz., (1) that forming part of the tissues, and 

 (2) that circulating as a ready supply for the nutritive demands 

 of the tissues. 



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

 food is suppplied 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 

 during starvation, continues to lose weight, and the quantity of 



