ALBUMINS OR PROTEINS. 217 



shown that the amino acids act very efficiently as sources of nitrogen. 

 The latter also called attention to the interesting fact that the molds will 

 only attack the a-amino acids, while other acids, with the amino groups 

 differently situated, are unacted upon. We may add that Aspergillus 

 niger will also act on the polypeptides produced from the a-amino acids, 

 as well as on the polypeptides which are not decomposed by trypsin; for 

 instance, glycyl-glycin and dileucyl-glycyl-glycin. This is not very unu- 

 sual, for we know that the animal organism possesses ferments in the cells 

 which are capable of breaking down compounds unattacked by trypsin. 

 That this assumption is correct, is evident from the previous description 

 of the behavior of individual polypeptides in the animal organism. 1 



Ammonium oxalate 2 has been observed as a metabolic end product in 

 mold activity, but only during growth with a supply of certain amino 

 acids; for instance, glycocoll, alanine, serine, aspartic . acid, glutamic acid, 

 and proline. On the other hand, no oxalic acid is produced from leucine, 

 phenylalanine, lysine, arginine, and histidine. Ammonia is very often 

 one of the end-products of mold and bacterial metabolism. We would 

 refer, for example, to the cleavage of urea by bacterial action with the 

 formation of ammonium carbonate. The different varieties of mold and 

 bacteria, moreover, produce unequal amounts of ammonia. Bacillus 

 mycoides, for instance, converts as much as forty-six per cent of the 

 nitrogen in albumin into ammonia. 3 



We might expect that carnivorous plants, unlike the Aspergillus niger 

 which we have just considered, would be able to assimilate directly the 

 amino acids and higher albuminous cleavage-products, synthesizing them 

 into albumin in the same manner as does the animal organism, i.e. without 

 preliminary decomposition. The metabolism of such plants has, unfortu- 

 nately, been studied but little, and we do not even know how they digest 

 albumin. That there are organisms in the vegetable world which are 

 only capable of forming albumin from its cleavage-products, is evident 

 from the researches of Beijerinck, 4 from which it appears that the conidial- 

 alga, Cystococcus humicola, the alga of the lichen, Physica parietina, with 

 which it lives in symbiosis, prepares peptones for the nourishment of the 

 latter. It would be interesting to study the true parasites and the sapro- 

 phytes from this point of view. 



Let us return to the behavior of the albuminous substances in the 

 intestine. Not all the cleavage-products of the proteins are absorbed. 

 A part is decomposed in another manner, and is lost for the further syn- 

 thesis of albumin in the animal body. Bacteria are present in the intes- 



1 Cf. p. 203. 



2 O. Emmerling: Zentr. Bakt. u. Parasitienkunde, II, 10, 273 (1903). 



3 E. Marchal: Zentr. Bakt. II, 1, 1753 (1895). 



4 Beijerinck: Bot. Zeit. 1890, No. 45, Zentr. Bakt. 13, 368 (1893). 



