DIGESTION. 85 



der various names in this group; as, the proteoses may be derived 

 from albumin, when they are called albumoses; or from globulin, 

 when the name globuloses is used. The proteoses are soluble in warm 

 water, acids, and the alkalies. They are only slightly diffusible and 

 not coagulated by the action of heat. Nitric acid produces a white 

 precipitate, which is colored yellow by heat and dissolved again. 

 When cool, the precipitate occurs again; this recurrence of the pre- 

 cipitate upon cooling is a distinctive feature of proteoses. Ammo- 

 nium sulphate precipitates proteoses and leaves the peptones in 

 solution. 



By the continued proteolytic action of the gastric juice, the 

 proteoses are changed into (3) peptones, the final, diffusible products 

 of gastric digestion. They are simply the result of a process of 

 hydration. 



The peptones are very diffusible, particularly in acid solution. 

 The utility and benefit to be derived from that characteristic is very 

 evident when we keep in mind the chief aim of digestion, which is to 

 render foodstuffs into soluble conditions so that they may be readily 

 absorbed and so become a component of the blood and eventually of 

 the tissues. 



The peptones are soluble in water, but not precipitated from 

 their aqueous solutions by the addition of acids or alkalies, or by boil- 

 ing. In fact, peptones are never coagulated by heat. They are not 

 precipitated by nitric acid, copper sulphate, ammonium sulphate, and 

 a number of other reagents usually held as precipitants of proteids. 



To differentiate albumoses from peptones, add a few drops of 

 salicyl-sulphonic acid to several cubic centimeters of the original fluid. 

 A white precipitate may indicate native proteid or proteoses. Boil, 

 then the proteoses dissolve, whereas the native proteid becomes 

 coagulated. Filter hot. If a precipitate forms in the filtrate on 

 cooling, it indicates proteoses. Filter off this precipitate and apply 

 the biuret test to filtrate. A rose-pink coloration indicates peptone. 



However, the chief and striking feature of peptones is their great 

 diffusibility. Other forms of proteid matter pass through animal 

 membranes with very great difficulty, if at all. 



When the proteids have been reduced to peptones, they are ready 

 for absorption into the blood through the capillary walls. However, 

 proteoses, the intermediate products, although less diffusible than 

 peptones, find their way, to some extent, also, through the capillary 

 walls. Experiment has demonstrated that pure proteoses, or even 

 peptones, introduced directly into the blood are more or less toxic, 



