FLUCTUATIONS IN BODY PROTEIN. 



83 



proximate equilibrium being reached on the seventh day. The total gain in the 

 seven days was 28.8 grams nitrogen, equivalent to 847 grams of fresh flesh, or 

 about 12 per cent of the surplus fed, equivalent to from 3.5 to 4 per cent of the 

 amount probably present in the body of the 35-kilogram dog. 



In order to retain this protein which was stored up in the body, however, it 

 was necessary to continue the heavier ration of 1,500 grams of meat. When, 

 in previous periods of the same series, a ration of 1,500 grams of meat was fol- 

 lowed by one of 1,000 grams and this by one of 500 grams, the protein pre- 

 viously stored up was rapidly katabolized again, as the following table shows : 



Loss of protein by dog — Voit. 





Date. 



Meat fed. 



Nitrogen 

 of feed. 



Nitrogen 

 of urine. 1 



Gain of 

 nitrogen. 





1863. 



Grams. 



Grams. 



Grams. 



Grams. 





Apr. 



11 



1,500 



51.0 



48.4 



+2.6 



Experiment No. 38 (last 3 days) 



Apr. 



12 



1,500 



51.0 



50.9 



+ .1 



Apr. 



13 



1,500 



51.0 



52.8 



-1 8 





Apr. 



14 



1,000 



34.0 



38.6 



-4.6 





Apr. 



15 



1,000 



34.0 



36.4 



-2.4 



Experiment No. 39 



Apr. 

 Apr. 



16 

 17 



1,000 

 1,000 



34.0 

 34.0 



36.4 

 36.1 



-2.4 

 -2.1 





Apr. 



18 



1,000 



34.0 



34.3 



— .3 





Apr. 



19 



1,000 



34.0 



35.2 



-1.2 





Apr. 



20 



500 



17.0 



23.7 



-6.7 





Apr. 



21 



500 



17.0 



20.4 



-3.4 



Experiment No. 40 



Apr. 

 Apr. 



22 

 23 



500 

 500 



17.0 

 17.0 



20.9 

 18.8 



-3.9 

 -1.8 





Apr. 



24 



500 



17.0 



17.4 



- .4 





Apr. 



25 



500 



17.0 



18.8 



-l.S 



The total loss of nitrogen from the body for the 12 days included in the 

 table is 31 grams, or an amount about equal to that stored up in passing from 

 the 500-gram to the 1,500-gram ration. 



This comparatively small store of rapidly katabolizable protein in the body 

 after liberal protein feeding Voit designated as circulatory protein, in distinc- 

 tion from the large mass of stable protein which he called organ protein. A 

 variety of other names, corresponding to more or less definite theories as to 

 the nature of the distinction between the two types of protein, have been pro- 

 posed by later investigators, such as stable and labile, organized and unorgan- 

 ized, tissue and reserve, living and dead, protein. Still others, notably Gruber, 3 

 explain the temporary storage of nitrogenous matter in the body as due to a 

 lag in the katabolism of protein, so that the splitting off of its nitrogen is not 

 complete within the ordinary 24-hour period. The facts, however, that the 

 nitrogen excretion follows in general the supply in the feed but that a tempo- 

 rary and limited storage of nitrogenous material in the body may result from 

 liberal protein feeding, are undisputed. 



FLUCTUATIONS IN BODY PROTEIN. 



It is a familiar fact that a fasting animal may live and continue 

 to perform the essential bodily functions for some time, while los- 

 ing daily a not inconsiderable amount of protein. To cite a single 

 striking example, Rubner observed in a fasting rabbit up to the time 

 of death, on the nineteenth day, a loss of 45.2 per cent of the com- 

 puted nitrogen of the body. 3 While this is an extreme case, neverthe- 



1 Computed from urea. 



2 Zeitschrift fur Biologie. vol. 42, p. 407. 



3 E. Voit. Zeitschrift fur Biologie, Vol. 41, p. 139. 



