PRODUCTS OF PROTEID DECOMPOSITION 89 



part of the nitrogen, 55 to 76 per cent, in proteids other than protamins is 

 in this form. 5, Varies within wide limits. 



"The sulfur, the amount of which varies greatly in different proteids, 

 is given off on hydrolysis as cystin, cystein, a-thiolactic acid, mercaptans, 

 and ethyl sulfid. 



"The nitrogen-containing products of hydrolysis of proteids may be 

 thus classified: 



I. Aliphatic. A. Containing no sulfur: 



1, Guanidin remainder. H 2 N.C : NHj (-f-ornithin=argenin); 



2, Monobasic monamido acids: glycocoll, alanin, amido-valerianic 



acid, leucin, serin; 



3, Dibasic monamido-acids: aspartic and glutamic; 



4, Monobasic diamido-acids: ornithin, lysin; 



B. Containing nitrogen and sulfur: Cystin, cystein; 

 II. Carbocyclic: phenylamidopropionic acid, tyrosin; 

 III. Heterocyclic : A. Pyrrol derivatives: pyrrolidin and oxypyrrolidin 

 carboxylic acids; 



B. Glyoxalin derivatives (?): histidin; 



C. Indole derivatives: indol, skatol, tryptophane." 



The amido-acids, although belonging to the different series f are, accord- 

 ing to Fischer's views, supposed to be combined into more and more com- 

 plex groupings. In the simplest combinations two or more molecules of 

 the same or of different amido-acids combine with the elimination of water. 

 This is the reverse of the hydrolytic process and results in Fischer's peptids. 

 Protamin, the simplest of the proteids, yields a relatively simple series of 

 amido-acids and according to Taylor's work, already referred to, is evidently 

 a polypeptid of comparatively complex structure. 



"All proteids except the protamins and some of the peptones contain 

 sulfur. One fraction of this, referred to as 'loosely combined' sulfur, is 

 given off as hydrogen sulfid by boiling with alkaline solutions. It is this 

 fraction which causes the formation of a brown or black color, or even a 

 black precipitate, .when a proteid is heated with a solution of caustic alkali 

 in the presence of lead acetate, in the 'sulfur test' for the proteids. The 

 second fraction is not separable in this manner, but only, as a sulfate, by 

 fusion with saltpeter and sodium carbonate, or, as a sulfid, by fusion with 

 caustic potash. The ratio of loosely combined sulfur to total sulfur varies 

 notably in different proteids, from in serum to f in hemoglobin. It would 

 appear from this constant difference in separability of different portions of 

 sulfur from proteids that the molecules of these substances must contain at 

 least two atoms of sulfur in different forms of combination. This conclu- 

 sion, is, however, invalidated by the fact that both cystin and cystein only 

 give off one-half of their sulfur, and that very slowly, by boiling with alka* 



