70 PHYSIOLOGICAL CHEMISTRY 



amino acids linked together in straight chains in a manner analogous to 

 the formation of simple peptides, such as glycyl-glycine. The molecu- 

 lar structure of the proteins is much too complex to be "explained upon 

 any such simple formation as that. There must be a variety of linkings, 

 since there is a varied assortment of decomposition products of totally 

 different structure. 



Many of these synthetic bodies respond to the biuret test, are pre- 

 cipitated by phosphotungstic acid, and behave, in other ways, as to 

 leave no doubt as to their protein characteristics. For instance, a 

 number of amino acids each possessing a sweet taste have been syn- 

 thesized in such a manner as to yield a polypeptide of bitter taste, a 

 well-known characteristic of peptones. From the fact that the poly- 

 peptides formed in the manner indicated have free acidic and basic 

 radicals we gather the explanation of the amphoteric character of true 

 proteins. 



For the benefit of those especially interested in such matters a photo- 

 graph of the Fischer apparatus (Fig. 24, page 74) used in the fractional 

 distillation, in vacuo } of the esters of the decomposition products of the 

 proteins, as well as micro-photographs and drawings of preparations of 

 several of these decomposition products (Figs. 21 to 33, pages 71 to 83) 

 are introduced. For the preparations and the photograph of the appa- 

 ratus the author is indebted to Dr. T. B. Osborne, of New Haven, Conn., 

 who has made many important observations upon the hydrolysis of 

 proteins. The reproduction of the crystalline form of some of the more 

 recent of the products may be of interest to those viewing the field of 

 physiological chemistry from other than the student's aspect. 



An extended discussion of the various decomposition products being 

 out of place in a book of this character, we will simply make a few general 

 statements in connection with the primary decomposition products. 



DISCUSSION OF THE PRODUCTS 



Ammonia, NH 3 . Ammonia is an important decomposition product 

 of all proteins and probably arises from an amide group combined 

 with a carboxyl group of some of the amino acids. It is possible that the 

 dibasic acids, aspartic and glutamic, furnish most of these carboxyl 

 groups. This is indicated by the more or less close relationship which 

 exists between the amount of ammonia and that of the dibasic acids 

 which the .several proteins yield upon decomposition. The elimination 

 of the ammonia from proteins- under the action of acids and alkalis is 

 very similar to that from amides like asparagine. 



Glycocoll (glycine), CH 2 (NH 2 )-COOH. Glycocoll, or amino acetic 



