RESEARCHES ON PROTEID METABOLISM. 149 



Voit himself has never clearly indicated what is meant by- 

 circulating proteid. Originally, at any rate, Voit looked 

 upon both blood-plasma and lymph as circulating proteid. 

 In his later writings, however, Voit speaks of the blood as an 

 organ, and confines the conception of circulating proteid to 

 the proteids of the tissue-juices, that is to say. of the lymph. 

 According to this theory, the greater part of the processes 

 of oxidation and disintegration must take place outside the 

 cells, whereas the work of Pfliiger and his pupils has shown 

 that the seat of oxidation is the living cell, and that little or 

 no metabolic changes take place within the blood or lymph. 

 According to Voit, the greater excretion of urea in a proteid- 

 fed animal is due to the fact that there is an increased cir- 

 culation of a fluid that is rich in proteids round the cells. 

 According to Pfliiger's view, however, the presence of a 

 greater or less amount of proteid in the nourishing medium 

 would not be the determining factor for the amount of urea 

 formed, which would be regulated simply and solely by 

 the condition of the cells themselves. At his suggestion 

 Schondorff has undertaken an experimental investigation of 

 the question (7). Departing from Schroder and Minkowsky's 

 experiments on the seat of formation of urea, Schondorff 

 led defibrinated blood alternately through the hind limbs 

 and the liver of another dog. He hoped in this way to get 

 the products of metabolism of the tissue of the limbs, and 

 then to convert these into urea by passing the blood through 

 the liver. 



In one set of experiments the blood from a dog that 

 had been starved for five days was led through the organs 

 of a well-fed dog. In these experiments he found that, 

 without exception, the urea in the blood was largely increased 

 at the end of the experiment. 



In a second series of experiments the blood of a fasting- 

 animal was led through the hind limbs and liver of a fasting- 

 animal. In these the amount of urea in the blood was un- 

 altered. 



In a third set, blood of a well-fed animal was led through 

 organs and liver of a fasting animal. In these cases the 

 amount of urea was always diminished. 



