SALIVA AND GASTRIC JUICE. 257 



It is obvious that the effect of the action of the gastric juice is to change 

 the less soluble proteid into a more soluble form, the change being either 

 completed up to the stage of peptone, the most soluble of all proteids, or 

 being left in part incomplete. This will be seen from the following tabular 

 arrangement of proteids according to their solubilities : 



Soluble in distilled water. 



Aqueous solutions not coagulated on boiling : 



Diffusible Peptone. 



Not diffusible Albumose. 



Aqueous solutions coagulated on boiling Albumin. 



Insoluble in distilled water. 



Readily soluble in dilute saline solutions (NaCl 1 per ) pi i r 



cent, ) f u 



Soluble only in stronger saline solutions (NaCl 5 to 10 ) M 



percent.) j My(M 



Insoluble in dilute saline solutions. 

 Readily soluble in dilute acid (HC1 0.1 percent.) in j Acid-albumin. 



thecold - -IcLt' 



Soluble with difficulty in dilute acid, that is at high ) 

 temperature (60 C. ) and after prolonged treatment V Fibrin, 

 only j 



Insoluble in dilute acids, soluble only in strong acids . Coagulated proteid. 



Milk when treated with gastric juice is first of all " curdled." This is the 

 result partially of the action of the free acid, but chiefly of the special action 

 of a particular constituent of gastric juice, of which we shall speak here- 

 after. The curd consists of a particular proteid matter mixed with fat ; and 

 this proteid matter is subsequently dissolved with the same appearance of pep- 

 tone, albumose, and parapeptone as in the case of other proteids. In fact, the 

 digestion by gastric juice of all the varieties of proteids consists in the con- 

 version of the proteid into peptone, with the concomitant appearance of a 

 certain variable amount of albumose and parapeptone. 



190. Circumstances affecting gastric digestion. The solvent action of 

 gastric juice on proteids is modified by a variety of circumstances. The 

 nature of the proteid itself makes a difference, though this is determined 

 probably by physical rather than by chemical characters. Hence in making 

 a series of comparative trials the same proteid should be used, and the form 

 of proteid most convenient for the purpose is fibrin. If it be desired simply 

 to ascertain whether any given specimen has any digestive powers at all, it 

 is best to use boiled fibrin, since raw fibrin is eventually dissolved by dilute 

 hydrochloric acid alone, probably on account of some pepsin previously 

 present in the blood becoming entangled with the fibrin during clotting. 

 But in estimating quantitatively the peptic power of two specimens of 

 gastric juice under different conditions, raw fibrin prepared by Gru'tzner's 

 method is most convenient. 



Portions of well-washed fibrin are stained with carmine and again washed to 

 remove the superfluous coloring matter. A fragment of this colored fibrin thrown 

 into an active juice on becoming dissolved, gives up its color to the fluid. 

 Hence if the same stock of colored fibrin be used in a series of experiments, and 

 the same bulks of fibrin and of fluid be used in each case, the amount of fibrin 

 dissolved may be fairly estimated by the depth of tint given to the fluid. Fibrin 

 thus colored with carmine may be preserved in ether. 

 17 



