STOMACHAL DIGESTION. 245 



juice. The paste thus obtained is not the final product ot 

 digestion ; it is what was formerly called chyme, before the 

 action of the gastric juice had been so minutely studied as 

 at present. This first stage is, however, followed by a 

 second, in which this pulp becomes completely liquefied; and 

 it is under this form only that the products of digestion pass 

 from the stomach into the intestine. 



This porphyration and succeeding liquefaction are accom- 

 panied by changes of color in the digested substances : thus 

 the white of the albumen of an egg becomes slightly yellow 

 or even red ; during the first stage blood becomes quite 

 black (vomiting of half-digested blood, in hemorrhage of the 

 stomach :' black haBtnatemesis) ; it is afterwards resolved into 

 a nearly colorless fluid. The final product of digestion by 

 the stomach is usually slightly yellowish. These changes in 

 color should be well known in order to avoid mistakes as to 

 the nature of the substances vomited. 



The final result of these different processes is the produc- 

 tion of new kinds of albumen, peptones or albumin o#68, 

 which are, as we have said, especially suited for absorption. 

 The peptones always preserve some feature of their original 

 substance : we can distinguish white of egg from that of 

 gelatine, fibrin e, etc. The length of time necessary for this 

 transformation depends on the nature of the aliments: thus 

 the white of egg is digested sooner when raw than when 

 cooked ; raw, or at least partially cooked, meat, is generally 

 much the easiest to digest, and should therefore be preferred 

 (setting aside the question of the entozoa). 



The study of the peptones or albuminoses is one of those 

 which have made the most progress of late years, owing to 

 the researches of Lehmann, Briicke, Meissner, Mulder, Schiff, 

 etc. It has been discovered, in the first place, that the 

 perfect peptone is a remarkably assimilable and endosmotic 

 product : its chief characteristic in a physiological point of 

 view is, that, if it be injected directly into the veins, it does 

 not reappear in the urine, showing that it is immediately 

 assimilated by the tissues. Chemically considered, it can be 

 precipitated neither by heat, acids, nor alkalies, but solely by 

 bichloride of mercury, Millon's reagent (nitrous or acid 

 nitrate of mercury) and some other rare reagents. The real 

 peptone thus consists of albumen which is not only dissolved, 

 but also transformed (chiefly by hydration, according to 

 Brinton). 



The real definite peptone is not, however, produced in the 



