DIGESTION AND ABSORPTION IN THE STOMACH. 693 



or less acidity. Too great or too small an acidity, however, will 

 retard the process; that is, there is for the action of the pepsin an 

 optimum acidity which lies somewhere between 0.2 and 0.5 

 per cent. Other acids may be used in place of the hydrochloric acid 

 for example, nitric, phosphoric, or lactic but they are not so 

 effective, and the optimum acidity is different for each; for phos- 

 phoric acid it is given as 2 per cent. 



The Pepsin-Hydrochloric Acid Digestion of Proteids. It has 

 long been known that solid proteids, when exposed to the action of a 

 normal or an artificial gastric juice, swell up and eventually pass into 

 solution. The soluble proteid thus formed was known not to be 

 coagulated by heat and was remarkable also for being more diffusible 

 than other forms of soluble proteids. This end-product of digestion 

 was formerly conceived as a soluble proteid with properties fitting 

 it for rapid absorption, and the name of peptone was given to it. It 

 was quickly found, however, that the process is complicated that in 

 the conversion to so-called "peptone" the proteid under digestion 

 passes through a number of intermediate stages. The intermediate 

 products were partially isolated and were given specific names, such 

 as acid-albumin, parapeptone, and propeptone. The present concep- 

 tion of the process we owe chiefly to Kiihne. This author believed 

 that the proteid passes through three general stages before reaching 

 the final condition of peptone. This view is indicated briefly by the 

 following schema : 



Native proteid. 



Acid albumin (syntonin) . 



Primary proteoses (protalbumoses). 



Secondary proteoses (deutero-albumoses). 



Peptone. 



The first step is the conversion of the proteid 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 in 

 general (see appendix), the syntonin is readily precipitated on 

 neutralization. In the beginning of peptic digestion, therefore, 

 if the solution is neutralized with dilute alkali, an abundant precipi- 

 tate of syntonin occurs. Later on in the digestion neutralization 

 gives no such effect the syntonin has all passed into a further stage 

 of digestion. Under the influence of the pepsin the syntonin under- 

 goes hydrolysis, with the production of a number of bodies which 

 as a group are designated as primary proteoses or protalbumoses.* 



* The products intermediate between the original proteid and the pep- 

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

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

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

 ate products are more appropriately designated as proteoses. 



