252 



PRACTICAL PHYSIOLOGY 



about four hours after breakfast, the latter consisting, one morning, 

 mainly of porridge or some similar proteid-poor diet, and on the next 

 morning mainly of some form of flesh or eggs. 



During starvation the excretion rapidly falls for the first few days, 

 and then remains constant for a week or two the starvation level after 

 which it again rises somewhat for a few days, this being followed by a 

 sudden fall accompanied by the death of the animal. The reason of 

 the primary fall is that no proteid food is being supplied to the vital 

 tissues, and, as a consequence of this, their metabolism becomes less 



Fig. 155. Improvised apparatus for estimation of urea. 



active, the energy necessary for life being meanwhile supplied by 

 the deposited fat. This latter ultimately becomes used up, however, 

 and then the proteids are called upon to supply the necessary energy, 

 and the urea excretion rises again. This disintegration of the vital 

 tissues cannot last for long, however, as the proteid tissues are 

 indispensable for life, and the animal dies. 



As regards the intermediate bodies between serum albumin and 

 globulin (as which the bulk of the proteids are absorbed into the portal 

 blood), and urea, very little is known. The majority of the inter- 

 mediate bodies have been already described in connection with the 

 tissues in which they are found, and all that remains is to string them 

 together in their proper sequence. 



By the hydrolysis of proteid in the intestine, amido acids and hexone 



