446 



PHYSIOLOGY. 



to the tissues. The amido-acids not used in tissue-building have 

 their nitrogen split off rapidly without loss of energy and converted 

 into urea, whilst the carbon residue is retained and utilized for the 

 production of energy in place of an equivalent energy value of fat 

 or carbohydrate. This decomposition takes place without that pre- 

 liminary conversion of the food proteid into tissue, contrary to the 

 usual prevalent view of Pflueger. (Abderhalden.) 



It is not known how much urea is formed in the liver, but it is 

 not far from half the amount of urea excreted. The intracellular 



Fig. 169. Uric-acid Crystals with Amorphous Urates. 

 (PuRDY, after PEYER.) 



ferments, which exist in nearly all the tissues, break up the proteids 

 of lymph into ammonia, which is also converted into urea by the 

 liver and by other tissues at present not known. 



During sleep the amount of urea excreted remains nearly the 

 same as when awake, but there is a diminution of carbonic acid 

 exhaled and of oxygen inhaled. These results are due to muscular 

 quietude. 



TIric Acid (C 5 H 4 N 4 3 ). This constituent is scarce in human 

 urine, hardly reaching 0.03 per cent, of its component solids.' Next 

 to urea, it is the product of excretion richest in nitrogen. It is very 





