111 DIGESTION IN THE MOUTH AND STOMACH 173 



syntonin, a proteose (formerly called by Schmidt-Miihlheim pro- 

 peptone), and a peptone. 



Syntonin is the first stage in the transformation of fibrin effected by the 

 gastric juice. When the liquid is slowly neutralised by successive drops ol' 

 sodium carbonate solution, the syiiloiiin precipitates, and can be- separated 

 by nitration. To convert boiled fibrin into syntonin, it is only necessary i< 

 use a simple solution of 1 per cent HC1, keeping it in the warm chamber for 

 1-2 days. But if a little pepsin be added to the acid, the conversion into 

 svnloiiin is much accelerated. Fluid egg-white, on the contrary, according 

 to Meissner, is converted into syntonin in a few minutes, at 40 J C. in simple 

 acid solution. 



The jinili'o*' differs from peptone in being precipitated with arctic acid 

 and potassium ferroc.yanide in the cold, and redissolved on heating. With 

 concentrated nitric acid there is also a precipitate, which disappears on 

 warming and comes bark on cooling. When treated with ammonium 

 sulphate, it is thrown out like all other proteins, and this is the best 

 method for separating and estimating the peptone, which remains in .-olntion 

 and passes through the filter. 



The jit'/itnix- which remains after separation of all the other proteins 

 from the digestive mixture, occurs in comparatively small quantities, showing 

 that gastric digestion is only partial, and is mainly a preparation of the 

 alimentary proteins for more complete digestion in the intestine. On add- 

 ing excess of caustic, soda or potash and a few drops of copper sulphate to the 

 mixture, it becomes pink (biuret reaction). But proteoses also give the 

 same reaction. In a faintly acid solution the peptones precipitate with 

 phosphotungstic and phosphomolybdic acid, which are therefore used for 

 the isolation of peptone from all the other proteins. It is to be noted that 

 commercial peptone contains a large amount of proteose and very little true 

 Peptone. 



The proteolytic or peptonising process by which fibrin, egg- 

 albumin, and the other proteins are transformed into syntouin, 

 proteose, and peptone has been the subject of numerous and 

 minute researches, particularly by Kiihne and his school ; these 

 are to be found in special treatises of chemical physiology. Here 

 we must confine ourselves to stating that the collective term 

 2iroteose includes several similar substances, which are dis- 

 tinguished from one another by various more or less definite 

 chemical characteristics, and that the end-products or peptones 

 must also be distinguished according to the nature of the original 

 protein from which they are derived. 



This sequence of the transformations of proteins is not due 

 to any specific action of the gastric enzyme : it can be obtained 

 artificially by prolonged boiling with plain water or, better, 

 dilute mineral acids, or by steam at high pressure, by treat- 

 ment with strong alkalies, lastly by the putrefactive processes 

 produced by bacteria. According to Neumeister, however, the 

 products obtained by these different methods are not identical. 



The gastric juice has a solvent action upon all proteins except 

 certain sclero-proteins. It transforms collagenic substances into 

 gelatin, which loses its faculty of coagulation, and is converted 

 into the so-called gelatin-peptone. Mucin, too, is converted into 



