ALBUMINOSE, OR PEPTONES. 247 



semble each other very closely is also undoubted ; but there are differences in .the chemi- 

 cal composition of the products of digestion of different principles, as well as differences, 

 which have lately been noted, as regards their behavior with reagents. 



Albuminose is a colorless liquid, with a feeble odor resembling that of meat. It is 

 not coagulable by heat, acids, or by pepsin ; a property which distinguishes it from almost 

 all of the nitrogenized principles of food. It is coagulated, however, by many of the 

 metallic salts, by chlorine, and by a solution of tannin, after it has been acidulated by 

 nitric acid. On evaporating albuminose to dryness, the residue consists of a yellowish- 

 white substance, resembling desiccated white of egg. This is soluble in water, when it 

 regains its characteristic properties ; but it is entirely insoluble in alcohol. 



Lehmann found a great similarity between the substances resulting from the digestion 

 of the various albuminoid bodies, and even those produced by the digestion of gluten, 

 chondrine, and gelatinous tissues. He was unable to obtain the peptones free from min- 

 eral substances. In the condition of greatest purity in which they have been obtained, 

 they have been found to be white, amorphous, odorless, with a mucous taste, very solu- 

 ble in water, and insoluble in alcohol. Their watery solutions redden litmus. They 

 combine readily with bases, forming neutral salts soluble in water. The differences be- 

 tween the various peptones are not as yet very well defined. Lehmann states that they 

 always contain the same proportion of sulphur that existed in the albuminoid substances 

 from which they are formed. According to this observer, the gastric juice transforms the 

 various nitrogenized alimentary principles into these liquid substances, which are not easily 

 coagulable and which present slight differences in chemical composition and general prop- 

 erties, varying with the principles from which they are formed. Those which have been 

 most particularly described are fibrin-peptone, albumen-peptone, and caseine-peptone. 



With even the imperfect knowledge which we have of the properties of albuminose, 

 it is evident that stomach-digestion, aside from its function in preparing certain articles 

 for the action of the intestinal fluids, does not simply liquefy certain of the alimentary 

 principles, but changes them in such a way as to render them endosmotic and provides 

 against the coagulation which is so readily induced in ordinary nitrogenized bodies. 

 Albuminose passes through membranes with great facility, and, as we have seen, is not 

 coagulable by heat or the acids. 



Another, the most important and the essential change which is exerted by the gastric 

 juice upon the albuminoids, is that by which they are rendered capable of assimilation 

 by the system after their absorption. The important fact that pure albumen and gela- 

 tine, when injected into the blood, are not assimilable, but are rejected by the kidneys, 

 was first demonstrated by Bernard and Barreswil. These observers found, also, that albu- 

 men and gelatine which had previously been digested in gastric juice were assimilated in 

 the same way as though they had penetrated by the natural process of absorption "from 

 the alimentary canal. The same is true of caseine and fibrin. These facts, showing that 

 something more is necessary in stomach-digestion than mere solution, point to pepsin as 

 the important active principle in producing the peculiar modifications so necessary to 

 proper assimilation of nitrogenized alimentary substances. The action by which the 

 albuminoids are thus modified in certain of their chemical and physical properties, as 

 well as dissolved, was formerly called catalytic; bat the signification of this term as 

 applied to the functions of digestion, assimilation, and nutrition, is so indefinite, that it 

 seems to be hardly more than a word used to express an absence of positive knowledge. 

 Certain it is, however, that the action of pepsin is essential to the changes which occur 

 in the albuminoid alimentary principles, resulting in the formation of what is known as 

 albuminose, or peptones; and the change into albuminose takes place in all nitrogenized 

 principles that are liquified in the stomach. This may occur even when the albuminoid 

 matters are somewhat advanced in putrefaction, and the gastric juice undoubtedly pos- 

 sesses antiseptic properties, which fact accounts for the frequent innocuousness of animal 

 substances in various stages of decomposition when taken into the stomach. 



