MAE"rJAL OF OATTLE-PEEBING. 211 



latter can be decided only after a careful consideration of 

 all the factors whicli may liave exerted an iniinence upon 

 the protein consumption. 



Attention has already been called to the fact that an in- 

 creased, excretion of water in the mine is accompanied by 

 an increased excretion of nitrogen also. A glance at the 

 table shows, however, that in these experiments the volume 

 of the urine increased constantly from one period to an- 

 other, and therefore cannot well have been the cause both 

 of an uicrease and decrease of the nreal nitrogen. 



A second point to be considered is the effect of pro- 

 longed work in altering the make-up of the body, especially 

 as regards the proportion of fat. It has already been 

 pointed out that muscular exertion canses an increased 

 destruction of the fat of the body, and that this was the 

 case in tliese experiments is shown by the gradual decrease 

 of the w^eiglit of the animal during the fii'st four periods, 

 as follows : 



Average weiglit in Period I 1 ,175 lbs. 



" '' '' 11 1,165 ^' 



JIXX .. .«...,... ......... i , xou 



*' " " IV 1,119 " 



' " '' '' V 1,140 '' 



Since, as shown by the table, the nitrogen excretion was 

 less than the supply, this loss of weight must have been 

 caused chiefly by a destruction of fat consequent upon the 

 increased work. 



But, as shown in Chapter YI., the body-fat tends to di- 

 minish the protein consumption, and, on the other hand, a 

 loss of fat by the body would have the opposite tendency ; 

 and we have therefore to consider whether the variations 

 in the protein consumption here observed can be explained 

 in this way. Obviously the increase in the first three pe- 



