DIGESTION AND ABSORPTION IN THE STOMACH. 787 



(metaproteins) in general (see Appendix), the syntonin is readily 

 precipitated on neutralization. In the beginning of peptic diges- 

 tion, therefore, if the solution is neutralized with dilute alkali, 

 an abundant precipitate of syntonin occurs. Later on in the 

 digestion, neutralization gives no such effect the syntonin 

 has all passed to a further stage of digestion. Under the in- 

 fluence of the pepsin the syntonin undergoes hydrolysis, with 

 the production of a number of bodies which, as a group, are 

 designated as primary proteoses or protalbumoses.* Although 

 several members of this group have been isolated and given 

 separate names, so much doubt prevails as to the chemical individ- 

 uality of these substances that it is best perhaps to regard them as a 

 group of compounds which under the continued influence of the 

 pepsin undergo still further hydrolysis with the formation of secon- 

 dary proteoses or deutero-albumoses. As compared with the primary 

 proteoses, the secondary ones are distinguished by a greater solu- 

 bility ; they require a stronger saturation with neutral salts to precipi- 

 tate them. (See Appendix.) The secondary proteoses undergo still 

 further hydrolysis, with the production of peptone, or perhaps it 

 would be better to say peptones. The peptones show still greater 

 solubility, and, in fact, peptone, in Kuhne's sense, is that compound 

 or group of compounds formed in peptic digestion which, while still 

 showing protein reactions (biuret reaction), is not coagulated by 

 heat nor precipitated when its solutions are completely saturated 

 with ammonium sulphate. According to the schema and descrip- 

 tion given above, the several stages in peptic digestion are repre- 

 sented as following in sequence. It should be stated, however, 

 that many authors consider that even in the beginning of the 

 digestion the protein molecule may be split into several complexes, 

 and that some of the end-products may be formed very early in 

 the action. The end-result of the action of the pepsin in the 

 stomach is the conversion of more or less of the protein of the 

 food into the simpler and more soluble peptones and proteoses. 

 The action of the enzyme is preparatory to the more complete 

 hydrolysis that takes place in the intestine under the influence of 

 the trypsin and erepsin, for, as we shall see, the protein of the food 

 is not absorbed into the blood as peptones, but suffers first a further 

 hydrolysis to amino-acids and peptids. While the pepsin is, there- 

 fore, a relatively weak proteolytic enzyme, it plays an important 

 role in initiating the splitting up of the protein molecule, and its 

 value in this respect is increased by the fact that it is adapted to 

 act upon proteins of all kinds and bring them to a stage suitable for 



*,The products intermedfate between the original protein and the pep- 

 tone are described in general as albumoses or as proteoses, according as one 

 takes the term protein or albumin as the generic name for the original sub- 

 stance. The term protein is generally used in English ; hence, the intermedi- 

 ate products are more appropriately designated as proteoses. 



