ACTION ON FATS, SUGARS AND AMYLACEOUS SUBSTANCES 199 



acidulated solutions. On evaporating peptones 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 proper- 

 ties, but is insoluble in alcohol. 



It is evident that the gastric juice, aside from its action in preparing 

 certain articles for digestion by the intestinal secretions, does not simply 

 liquefy certain of the alimentary matters, but changes them in such a 

 way as to render them osmotic and provides against the coagulation 

 which is so easily induced in other proteids. Peptones readily pass 

 through membranes. 



Another, the most important and the essential change exerted by 

 the gastric juice on proteids, is that by which they are rendered capa- 

 ble of assimilation by the system after their absorption. Pure albumin 

 and gelatin, injected into the blood, are not assimilable and are thrown 

 off by the kidneys ; but albumin and gelatin that have been digested 

 in gastric juice are 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 casein and fibrin. The action of pepsin is 

 essential to the changes that occur in the albuminous alimentary mat- 

 ters, resulting in the formation of the various peptones ; and the change 

 into peptones takes place in all nitrogenous substances that are dis- 

 solved in the stomach. This may occur even when the albuminous 

 matters are somewhat advanced in putrefaction ; and the gastric juice 

 possesses antiseptic properties, which accounts for the frequent innocu- 

 ousness of animal substances in various stages of decomposition when 

 taken into the stomach. 



The change of proteids into peptones in the stomach is not direct ; 

 but the intermediate changes, probably, simply are hydrolytic processes. 

 The proteids are changed by the gastric juice into a class of substances 

 known as proteoses, which includes products from the albumins, globu- 

 lins, gelatins etc., in their various stages of change. The actual con- 

 ditions between the proteids of food and peptones, treating them as 

 albumin, probably are the following : Albumin is first converted into 

 parapeptone (acid-albumin, syntonin); this is converted into propeptone, 

 which includes (a) protoalbumose, (b) heteroalbumose and (c) deutero- 

 albumose. These finally are converted into peptone and their digestion 

 is complete. 



Action on Fats, Sugars and Amylaceous Substances. Most of the 

 fatty constituents of food are liquefied at the temperature of the body ; 

 and when taken in the form of adipose tissue, the vesicles in which the 

 fatty matters are contained are dissolved, the fat is set free, is melted 

 and floats in the form of drops of oil on the alimentary mass. The 



