298 THE PROCESS AND THE PRODUCTS OF GASTRIC DIGESTION. 



of vitellin, chondrigen, collagen, and elastin, though with difficulty, are 

 in the same way converted into albumoses and peptones; while neuro- 

 keratin, keratin, and nuclein remain undigested. 



During the digestion of albumin, absorption of heat takes place, 

 demonstrable by the thermometer. Accordingly the temperature of the 

 chyme in the stomach falls, in the course of two or three hours, from 

 0.2 to 0.6 C. 



The coagulated proteids may be designated the anhydrids of the 

 liquid proteids and the latter in turn the anhydrids of the peptones. 

 Thus the peptones represent the highest possible stage of hydration of 

 the proteid bodies. 



Peptones may also be obtained from proteids with the aid of such agents as 

 usually cause hydration, particularly by treatment with superheated steam vapor, 

 through the action of strong acids, caustic alkalies, ferments of putrefaction and 

 some other ferments, as well as by ozone. 



The proteid anhydrids may be reconverted from this stage of hydra- 

 tion by the abstraction of water. 



By heating with acetic-acid anhydrid at a temperature of 80 C. peptone is 

 transformed into syntonin. Also by heating to a temperature of 170 C., through 

 the action of the galvanic current in the presence of sodium chlorid, and through 

 the action of alcohol together with salts, peptone is retransformed into albumin. 

 Albumose was thus first seen to result from fibrin-peptone. 



Properties of Peptones. (i) They are readily and completely soluble 

 in water. ( 2 ) They diffuse readily through membranes , more readily than 

 propeptones. (3) They also filter much more readily than albumin 

 through the pores of animal membranes. (4) From a mixture of pep- 

 tone, propeptone, albumin and pepsin, first neutralized and then feebly 

 acidulated with acetic acid, neutral ammonium sulphate added in excess 

 precipitates everything except peptone. (5) Peptones are not precipi- 

 tated by boiling, or by nitric acid, or acetic acid and potassium ferro- 

 cyanid, or by acetic acid or by saturation with sodium chlorid. (6) They 

 are precipitated by phosphotungstic, by phosphomolybdic acid, and by 

 biliary acids; precipitated by tannic acid, they are redissolved in an 

 excess. Other precipitating agents are mercuric chlorid and nitrate, 

 mercuric iodid , potassium iodid . ( 7 ) They yield all of the color-reactions 

 of albumin. (8) With sodium hydrate and copper sulphate in the cold, 

 they give a purple-red color (biuret-reaction). 



The biuret-reaction is yielded also by propeptone, as well as by a proteid body, 

 the so-called alkophyr, formed coincidently in the process of artificial digestion and 

 soluble in strong alcohol. Gelatin-peptone and gelatin are precipitable by tri- 

 chloracetic acid, while albumin-peptone is redissolved in an excess of this acid. 

 This is a useful means of differentiating these peptones. The peptones of the 

 various proteid bodies are distinguished by the amount of sulphur they contain, 

 with some of which this substance is but* loosely combined, while with others 

 it is firmly united. All have a disagreeable and bitter taste. 



In order to demonstrate the rapidity with which fibrin is digested by the 

 gastric juice, Grunhagen places in a funnel the fibrin that has been saturated with 

 0.2 per cent, hydrochloric acid, moistens it with digestive fluid and notes the 

 rapidity with which the fibrin gradually melts away, drop by drop, and finally is 

 entirely dissolved. Grutzner stains the fibrin with carmine, saturates it with o.i 

 per cent, hydrochloric acid, and places it in the digestive fluid. The more rapidly 

 the latter becomes stained uniformly red, in consequence of digestion of the fibrin, 

 the more energetic, naturally, is the digestive action. 



Quantitative Estimation of the Activity of Pepsin. Of a solution of egg-albumin 

 (3 grams in 160 cu. cm. of 0.4 per cent, hydrochloric acid) two specimens of 10 



