DIGESTION. 133 



(NEUMEISTER), and according to KUHNE and NEUMEISTER the 

 amido-acids found in the specified cases as products of digestion 

 were derived from the contamination of the gastric juice employed. 



Action of Pepsin Hydrochloric Acid on other Bodies. The gela- 

 tine-forming substance of the connective tissue, of the cartilage and 

 of the bones, from which last the acid only dissolves the inorganic 

 substances, is converted into gelatine by digesting with gastric 

 juice, The gelatine is further changed so that it loses its property 

 of gelatinizing and is converted into a so-called gelatine peptone 

 (see page 38). True mucin (from the submaxillary) is dissolved 

 by the gastric juice and yields a substance similar to peptone and a 

 reducible substance similar to that obtained by boiling with a 

 mineral acid. Elastin is dissolved more slowly and yields the 

 above-mentioned substance (page 36). Keratin and the epidermis 

 formation are insoluble. Nuclein is not dissolved and the cell- 

 nucleus is therefore insoluble in gastric juice. The animal cell- 

 membrane is, as a rule, more easily dissolved the nearer it stands to 

 elastin, and it dissolves with greater difficulty the more closely it is 

 related to keratin. The membrane of the plant-cell is not dissolved. 

 The oxyhcemoglobin is changed into haematin and acid albuminate, 

 the latter undergoing further digestion. It is for this reason that 

 blood is changed into a dark-brown mass in. the stomach. The 

 gastric juice does not act on fat, but, on the contrary, on fatty 

 tissue in which it dissolves the cell-membrane, setting the fat free. 

 Human gastric juice, according to LEUBE, can convert cane-sugar 

 into grape-sugar. Pepsin hydrochloric acid does not seem to take 

 any part in the decompositions and cleavages, which the carbo- 

 hydrates may undergo in the stomach. 



Pepsin alone, as above stated, has no action on proteids, and an 

 acid of the intensity of the gastric juice can only very slowly, if at 

 all, dissolve coagulated albumin at the temperature of the body. 

 Pepsin and hydrochloric acid together not only act more quickly, 

 but qualitatively they act otherwise than the acid alone. If liquid 

 proteid is digested with hydrochloric acid of 2 p. m., it is con- 

 verted into acid albuminates; but if the acid is replaced by pepsin, 

 the formation of syntonin takes place essentially slower under the 

 same conditions (MEISSNER). From this it is inferred that a part 

 of the hydrochloric acid is combined with the pepsin, and we have 



