LEO F. RETTGER 221 



vegetable protein which represented 60 per cent of the protein molecule. The defi- 

 ciency may be partly explained, according to him, by a loss in the process of hydrolysis 

 and isolation. It may also be due to the occurrence in the protein of modified amino 

 or amide substances which resist isolation and identification. 



Amino acids are crystallizable and, with very few exceptions, quite soluble in 

 water. They behave as both weak acids and bases, and form salts with them. 



The primary amino acids react with formaldehyde by a process in which the 

 amino groups are condensed and lose their basic character. This constitutes the under- 

 lying principle of the Sorensen method of determining the quantity of primary amino 

 acids in any given solution, as, for example, peptone broth cultures of bacteria. 



The amino group is readily destroyed by nitrous acid, and by the quantity of ni- 

 trogen gas evolved in the reaction the amount of amino acid or acids may be esti- 

 mated (Van Slyke method). 



The occurrence of chromatin or nuclear material in the bacterial cell can no longer 

 be doubted. Nishimura' and Galeotti^ demonstrated the presence of nucleins in bac- 

 teria. The former also isolated the xanthin bases, xanthin, guanin, and adenin. Nucleic 

 acids were obtained from the tubercle bacillus by Ruppel,^ from the diphtheria ba- 

 cillus by Aronson,'^ and from Bad. coli by Carega.^ More recently Johnson and Brown^ 

 isolated thymine and cytosine from the tubercle bacillus as the pyrimidines of the 

 nucleic ("tuberculinic") acid of this organism. At about the same time the purin 

 bases, guanin and adenin, were demonstrated by Long^ in the tubercle bacillus, 



ANALYTICAL PROCESSES BROUGHT ABOUT BY BACTERIA 



Through the agency of certain enzymes the complex protein molecule is split up 

 into its numerous amino acids and perhaps some other nitrogenous constituents. The 

 proteolytic enzyme or enzymes concerned differ from ordinary pepsin in that as a rule 

 the hydrolysis is carried beyond the proteose and complex polypeptide stage. They 

 differ also from trypsin of the animal body in that they act over a wide range of H- 

 ion concentration, that is, on the acid as well as alkaline side of pH 7.0. However, the 

 hydrolytic products are, at least in a large measure, like those of trypsin, and are 

 chiefly amino acids, including ordinary tryptophane (a-amino jS-indol propionic 

 acid). 



In this process of proteolysis some of the nitrogenous products are again utilized 

 by the organisms to furnish energy for growth and new cell substance. We must as- 

 sume that a synthetic process goes on simultaneously with the analytic. 



Further decomposition of amino acids by bacteria is altogether different from what 

 takes place in the animal body, and an entirely different group of final cleavage prod- 

 ucts is formed. Indol, skatol, and phenol are common among the strictly bacterial 



' Nishimura, T.: Arch. f. Hyg., 18, 318. 1893. 



' Galeotti, G.: Zlschr.f. phys. Chemie, 25, 48. 1898. 



3 Ruppel, W. G.: ibid., 26, 218. 1898. 



■•Aronson, H.: Arch.f. Kinderh., 30, 23. 1900. 



s Carega, A.: Cenlralbl. f. Bakteriol., Abt. I, 34, 323, 1903. 



* Johnson, T. B., and Brown, E. B.: Am. Rev. Tuberc, 7, 285. 1925. 



'Long, E. R.: ibid., 4, 842. 1920. 



