ALBUMINS OR PROTEINS. 263 



liver is practically the only organ in the body producing urea, we must 

 conclude that the nitrogenous cleavage-products, whether ammonia or 

 any compound containing the CO . NH 2 group, formed by the cell func- 

 tions, would have to be transported to the liver, and there acted upon. 

 Here is another large gap in our knowledge concerning the decomposition 

 of albumin in the tissues, which we do not seem able to bridge over at 

 present. Hypotheses have, therefore, been advanced here, which we 

 have already discussed under the formation of urea and uric acid. 



If we accept the foregoing explanation of the decomposition of albumin 

 in the tissues, we must naturally expect that the presence of some of the 

 amino acids which have been designated as representing transition stages 

 may be detected. As a matter of fact, certain observations do indicate 

 the presence of amino acids in the intermediate metabolism of albumin. 

 We will, moreover, state, in order to prevent any misapprehension, that 

 when the proteins are broken down by the cells into the amino acids, 

 further decomposition need not necessarily immediately follow, any more 

 than that the muscles must immediately consume any dextrose which 

 may be presented to them. Just as the muscles produce their glycogen 

 from dextrose, so the cells undoubtedly utilize the decomposition-products 

 according to their requirements, at one time decomposing them further, 

 and at another time linking them together into chains, thus utilizing the 

 proteins thereby formed as building material for the contents of their 

 own cells, or for forming new cells. Every individual cell must build up 

 its own albumin, in the same manner as the intestine, and form its 

 own peculiar albumin from its own particular nourishment, the serum- 

 albumin. This probably takes place in much the same way as in the 

 intestine, with its digestive ferments furnished by the glands. The 

 body cells, also, probably supply themselves with the necessary materials 

 for their cell requirements by breaking down the proteins into simpler 

 portions. Polypeptides and amino acids very likely appear as transition 

 products in the intermediate metabolism of albumin. Just as the intes- 

 tines do not decompose the albumins entirely into the lowest cleavage- 

 products, so we need not expect the tissue-cells to decompose all of the 

 albumin into its simplest components. These cells also probably only 

 decompose the proteins to the point where they can be utilized to recon- 

 struct new albumins. 



The assumption that cell-metabolism also produces amino acids, has 

 been supported by the fact that it is possible to protect certain of these 

 amino acids from being acted upon further by the administration of 

 specific compounds which possess the faculty of uniting with them, and 

 thus to recover them. In this way the presence of cystine in dogs has been 

 verified by introducing phenyl halides (brom-, chlor-, or iodo-benzene) 

 into the animal. By feeding benzoic acid to mammals, we obtain a com- 



