776 PHYSIOLOGY OF DIGESTION AND SECRETION. 



that in the conversion to so-called "peptone" the protein under 

 digestion passes through a number of intermediate stages. The in- 

 termediate products were partially isolated and were given specific 

 names, such as acid-albumin, parapeptone, and propeptone. The 

 present conception of the process we owe chiefly to Ktihne. This 

 author behoved that the protein passes through three general stages 

 before reaching the final condition of peptone. This view is indi- 

 cated briefly by the following schema: 



Native protein. 



Acid albumin (syntonin). 



Primary proteoses (protalbumoses). 



Secondary proteoses (deutero-albumoses). 



Peptone. 



The first step is the conversion of the protein to an acid albumin. 

 This change may be considered as being chiefly an effect of the hy- 

 drochloric acid, although in some way the combined action of the 

 pepsin-hydrochloric acid compound is more effective than a solution 

 of the acid alone of the same strength. Like the acid albumins 

 (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 Kiihne'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- 



* The products intermediate 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. 



