4 oo CHEMISTR Y OF THE DIGESTIVE PROCESSES. 



From this variable material products showing minute variations are 

 produced, of which we only know that they are more soluble than the 

 mother substance, less easily thrown out of solution by various precipit- 

 ants, and to a certain slight extent are capable of diffusing through 

 membranes. 



Here our knowledge at present stops. In spite of most laborious 

 researches on the subject by a host of observers, we know no more of 

 the structure of any save the final decomposition products of proteid 

 digestion than we do of the proteids themselves. Certain products have 

 been isolated at various intervals in the progress of digestion of proteids, 

 which show that the process gives rise to several intermediate bodies, 

 ever increasing in solubility towards precipitants as they are formed 

 nearer the end of the process ; and it may be it is a probable inference 

 from analogy that these substances *re simpler than the proteids from 

 which they originate, but as yet the simplest of them is too complex 

 for our fragmentary knowledge to give any indication of its structure. 

 Nor is there any knowledge of the relationship of these several stages of 

 proteid digestion to one another. 



It is very probable that the process of proteid digestion, like all the 

 other digestive processes, is one of continuous absorption of the elements of 

 water or hydrolysis. 



This is shown by the following observations : (1) One of the commonest 

 agents employed in organic chemistry for the purpose of hydrolysing a 

 substance is boiling with a dilute mineral acid, or subjecting in closed 

 vessels to the action of superheated steam. On submitting proteids to the 

 prolonged action of these reagents, products closely resembling or identical 

 with those produced by the action of the proteolytic enzymes are obtained. 

 (2) A small but decided increase in weight has been observed in the formation 

 of peptone from proteid. 1 (3) Peptones can be converted artificially back 

 into proteids by the use of reagents which are essentially dehydrating in 

 their action. If fibrin- peptone be heated for an hour with acetic anhydride, 

 the excess of anydride distilled off along with acetic acid formed in the pro- 

 cess, and the residue treated with hot water, the greater part of it dissolves. 

 When this solution is dialysed, there remains behind in the dialyser a solution 

 which coagulates on boiling, and is precipitable by nitric acid or potassium 

 ferrocyanide. Also, peptone heated for some time to 140 C. yields a substance 

 which on solution in water shows more of the properties of a native albumin 

 than of a peptone. 2 



Other theories regarding the digestion of proteids are (1) That the proteids 

 are polymers of the peptones, and that the process of digestion is a process of 

 depolymerisation, 3 (2) that proteids and peptones are simply different isomeric 

 forms of the same substance, and (3) the micellar theory, 4 according to which 

 the proteids are composed of micelli, which are a kind of second order of 

 molecule much more complex in structure. On peptonisation, the proteid first 

 breaks up into its constituent micelli, then the micelli fall into molecules, in 

 the chemical sense of the word, and these molecules are the peptone molecules. 



1 A. Danilewski, CentralU. f. d. med. Wissensch., Berlin, 1880, No. 42, S. 769. 



2 Hemiinger, Compt. rend. A cad. d. sc., Paris, 1878, tome Ixxxvi. p. 1464; Hofmeister, 

 Ztsclir. f. physiol. Chem., Strassburg, 1878, Bd. ii. S. 206 ; Neumeister, Ztschr. f. Biol., 

 Miinchen, 1887, Bd. xxiii. S. 394. 



8 Maly, Arch. f. d. ges. Physiol., Bonn, 1874, Bd. ix. S. 585; ibid., 1879, Bd. xx. 

 S. 315 ; Herth, Ztschr. f. physiol. Chem., Strassburg, Bd. i. S. 277 ; Monatsh. f. Chem., 

 Wien, Bd. v. ; Poehl, Ber. d. deutsch. diem. Gescllsch., Berlin, 1881, S. 1355; 1883, S. 

 1152 ; Loew, Arch. f. d. ges. Physiol., Bonn, 1883, Bd. xxxi. S. 393. 



4 Griessmayer, Jahresb. ii. d. Fortschr. d. Thier-Chem., Wiesbaden, Bd. xiv. S. 26. 



