150 SCIENCE PROGRESS. 



From these experiments SchondorfT draws the following 

 conclusions : — 



i. The extent of proteid metabolism depends on the 

 nutritive condition of the cell and not on the amount of pro- 

 teid contained in the circulating tissue-juices. 



2. The amount of urea contained in the blood varies 

 with the condition of the animal. The blood of a fasting 

 dog contained 0*0348 per cent, urea as a minimum. The 

 maximum amount of urea in the blood of a fed dog was 

 0*1529 per cent. 



3. Urea is manufactured in the liver out of nitrogenous 

 substances which have been produced in the other organs. 

 These substances are probably salts of ammonia. 



Pfliiger then would explain the course of events in star- 

 vation as follows : An animal cell desires above all things 

 proteid food, and when it can get enough of this feeds upon 

 nothing else. Only when proteid is lacking will it take up 

 fat or carbohydrate. Thus, while a dog is fed on a rich 

 mixed diet, he lives practically on proteid alone, storing up 

 the fats and carbohydrates of the food as fat. If food be 

 now withdrawn, the animal must live either at the expense 

 of his own living tissues (proteids), or must attack the 

 stored-up fats in his body. The latter, as a matter of fact, 

 takes place. The animal now spares the precious proteid 

 and lives on the fat of his own body. Hence comes the 

 great fall in the excretion of urea that is observed in starva- 

 tion, the consumption of proteid sinking to the indispensable 

 minimum. If now a proteid meal be given, the cells of the 

 body return to their former way of living, and satisfy as 

 much of their needs as possible at the expense of proteid, 

 so that the urea excretion rises almost in proportion to the 

 food given. In order to attain nitrogenous equilibrium, it 

 is necessary to give the cells enough proteid for their total 

 requirements, i.e., two or three times as much as would cor- 

 respond to the nitrogenous excretion during hunger. 



These views of Pfliiger have the double advantage of 

 being simple and at the same time in accord with the 

 observed facts of experiment, and will no doubt displace 

 the hazy and indefinite conception which has given birth to 



