472 DIGESTION. 



they tend to retard it. The action of metallic salts in different cases 

 can be explained in various ways, but they often seem to form with pro- 

 teins insoluble or difficultly soluble combinations. The alkaloids may 

 also retard the pepsin digestion (CHITTENDEN and ALLEN 1 )- A very 

 large number of observations have been made in regard to the action 

 of foreign substances on artificial pepsin digestion, but as these observa- 

 tions have not given any direct result in regard to the action of the 

 same substances in natural digestion, as well as upon secretion and 

 absorption, we will not discuss them here. 



The Products of the Digestion of Proteins by Means of Pepsin and Acid. 

 In the digestion of nucleoproteins or nucleoalbumins an insoluble residue 

 of nuclein or pseudonuclein always remains, although under certain 

 circumstances a complete solution may occur. Fibrin also yields an 

 insoluble residue, which consists, at least in great part, of nuclein, 

 derived from the form-elements inclosed in the blood-clot. This residue 

 which remains after the digestion of certain proteins was called dyspep- 

 tone by MEISSNER. This name is therefore not only unnecessary but 

 indeed erroneous, as this residue does not consist of bodies related to the 

 peptones. In the digestion of proteins, substances similar to acid albu- 

 minates, parapeptone (MEISSNER 2 ), antialbumate, and antialbumid 

 (KUHNE), may also be formed. On separating these bodies the filtered 

 liquid, neutralized at boiling-point, contains proteases and peptones in 

 the old sense, while the so-called KUHNE true peptone and the other 

 cleavage products are obtained only after a longer and more intense 

 digestion. The relation, between the proteoses, changes very much in 

 different cases and in the digestion of the proteins. For instance, a larger 

 quantity of primary proteoses is obtained from fibrin than from hard- 

 boiled egg albumin or from the proteins of meat; and the different 

 proteins, according to the researches of KLUG, 3 yield on pepsin diges- 

 tion unequal quantities of the various digestive products. In the diges- 

 tion of unboiled fibrin an intermediate product may be obtained in the 

 earlier stages of the digestion a globulin which coagulates at 55 C 

 (HASEBROEK 4 ) . For information in regard to the different proteoses 

 and peptones which are formed in pepsin digestion see pages 127 to 136. 



Action of Pepsin-Hydrochloric Acid on Other Bodies. The gelatin- 

 forming substances of the connective tissue, of the cartilage, and of the 



1 Studies from the Lab. Physiol. Chem. Yale University, 1, 76. See also Chitten- 

 den and Stewart, ibid. 3, 60. 



2 The works of Meissner on pepsin digestion are found in Zeitschr. f. rat. Med., 7, 

 8, 10, 12, and 14. 



3 Pfliiger's Arch., 65. 



4 Zeitschr. f. physiol. Chem., 11. 



