164 LECTURE VIII. 



themselves. We are, however, aware that many ferments occur in the 

 tissues, which are far more energetic in metabolic processes, and act 

 in another direction, than the digestive ferments. Many of the 

 results obtained are undoubtedly due to the interaction of these tissue- 

 ferments. We are now able to obtain the digestive fluids in purest form, 

 thanks to the excellent methods originated by Pawlow l and his students. 

 It is possible, on the one hand, to prepare a small special stomach, that is, 

 a pouch obtained by tying up a part of the walls of the stomach so as to 

 form a blind-sack, from which the pure gastric juice may be obtained with- 

 out the least admixture of any food residues. On the other hand, we can 

 obtain absolutely pure pancreatic juice, clear as water, by making a 

 pancreatic fistula, i.e., by grafting into the abdominal wall that part of the 

 mucous membrane of the duodenum at which the pancreatic duct enters. 

 As we shall see later, this fluid is inactive when the piece of intestinal 

 mucous membrane carrying the papilla is cut away. It must first be 

 made active preferably by the addition of intestinal juice. It is only 

 possible to obtain absolutely correct results by utilizing such ferment 

 solutions. 



Amino acids do not immediately appear when the proteins edestin, 

 for example are undergoing digestion. We observe first of all that the 

 albumin is dissolved. 2 We notice at the same time that the digestion 

 mixture contains dialyzable substances which are not amino acids. 

 The digesting mixture may even be boiled without causing coagulation. 

 It has been held that the protein molecule by hydrolytic cleavage is 

 decomposed into products with lower molecular weights; the higher of 

 these are known as albumoses, from which in turn peptones are formed. 

 There is no sharp distinction between these two classes. Strictly speak- 

 ing, the conception of albumoses and peptones is not a chemical, but a 

 biological one, and we shall treat of them here as forming one class, and 

 drop the term "albumose." It represents, instead of certain chemical 

 individuals, a group of compounds which exist temporarily in a similar 

 condition. For the present, these names do not signify much to us. 

 Not content with this distinction of the two groups of substances, 

 scientists have classified them according to their solubility relations, - 

 according to the extent to which they may be precipitated, etc., thereby 

 designating them with new names. It has also been found that the 

 peptones obtained from different proteins are not identical, so that they 

 have been named according to the protein from which they are formed. 



1 J. P. Pawlow: Ergebnisse d. Physiol. (Asher and Spiro) 1, 246 (1902). 



* The earliest observations on tryptic digestion were made by Corvisart: Gaz. Heb- 

 dom. Nos. 15, 16, 19 (1857). W. Kiihne: Virchow's Arch. 39, 130 (1867). Cf. also 

 E. Abderhalden: Z. physiol. Chem. 44, 17 (1905). 



