A HISTORY OF METABOLISM 69 



In another experiment, using a normal dog, the intake of nitrogen 

 contained in protein was 180.52 gm. and the outgo 180.96. In three of 

 the five experiments the whole of the ingested nitrogen in meat was re- 

 covered in the urine and feces. This did not support the idea that protein 

 nitrogen is eliminated in gaseous form through the lungs and the skin. 



Bischoff stated that a part of the protein metabolism must be used 

 for the growth of the hair and the epidermis, and this would still further 

 lessen the possibility of its elimination as a gas in the experiments as 

 computed 'by Voit. 



This work of Voit was carried further and published by Bischoff 

 (born 1807) and Yoit (/) in 1860 under the title, "Die Gesetze der Er- 

 nahrung des Fleischfressers," of which the following is an abstract : 



"We propose to consider nutrition and the energy relations therein 

 involved as they concern the animal organism, much of which may seem 

 to be theoretical and therefore of little importance but which really 

 embodies the sum of the recently acquired knowledge concerning energy 

 and matter and which in part is concerned with our own observations." 



All the experiments were done by Dr. Voit with the assistance of a 

 laboratory servant and it is Dr. Bischoff's opinion "that the numberless 

 analyses, the combustions and nitrogen, determinations of various foods, 

 of feces, etc., could not have been done with greater care or more tireless 

 zeal than they were done by Dr. Voit." 



They do not believe that all the protein of the ingesta must first be 

 organized into the material of living cells before it can be metabolized, 

 but rather that the fluid protein of the blood penetrates living cells there 

 to be destroyed. 



A dog was given 250, 500, 800, 1000 gm. of meat and still lost body 

 nitrogen. With 1800 gm. of meat the urea nitrogen was equal to that of 

 the food and when 2000 and 2500 gm. of meat were given the dog added 

 flesh to his body, but this had hardly begun before the quantity of urea 

 increased in the urine because the mass of metabolizing body tissue had 

 been increased. The dog would not eat more than 2500 gm. of meat. 



The methods of calculation of the metabolism used by Bischoff and 

 Voit were much more crude than those of Bidder and Schmidt who pre- 

 ceded them. But the records of 'the protein metabolism, as measured in 

 the nitrogen in the meat ingested and in that of the urine and the feces, 

 are the classical observations on the subject. 



In one experiment a dog weighing 35 kg. was given 31.6 kg. of rye 

 bread during a period of 41 days. The animal received 405.29 gm. of 

 nitrogen in the bread and eliminated 531.67 gm. in the urine and feces, 

 indicating a loss of body nitrogen of 126.38 gm., which corresponded to 

 a loss of "flesh" amounting to 3717 gm. Though the food was evidently 

 insufficient, the dog appeared well nourished and active at the end of the 

 experiment. His actual loss in body weight was only 690 gm. during 



