336 CHEM1STR Y OF THE DIGESTIVE PROCESSES. 



in twenty-four hours, but caused coagulation of fresh milk of neutral 

 reaction in one to three minutes. 



Such a solution of purified rennin behaves essentially differently in 

 its reactions from a proteid solution. It is not coagulated by heat, 

 does not give the xanthoproteic reaction, and is not precipitated by 

 alcohol, tannin, iodine, or neutral acetate of lead ; it is, however, pre- 

 cipitated by basic acetate of lead. 



THE PANCREATIC ENZYMES. 



The pancreatic juice of all vertebrates in which it has been tested 1 

 contains three distinct enzymes, each of which acts on a different class 

 of the three great divisions of foodstuffs. 2 In the invertebrates generally, 

 the place of the pancreas is taken by the so-called liver, hepato-pancreas, 

 or digestive gland. This usually contains enzymes, capable collectively 

 of attacking all three classes of foodstuffs, and with varying reaction ; 

 so that this organ may be considered as taking the place of the combined 

 digestive glands of the vertebrates. 3 



The different enzymes of the pancreas do not appear equally early in 

 life ; the pancreatic diastase, amylopsin, is not found at birth, but first 

 appears a month or more afterwards. 4 The proteolytic ferment, trypsin, 

 is found during the last third of foetal life. 5 No similar information is 

 on record regarding the fat-splitting ferment, steapsin. 



The relative amounts of the different enzymes in pancreatic juice 

 vary considerably. In passing from a flesh to a bread-and-milk diet, the 

 proteolytic activity is said to diminish while the diastatic activity in- 

 creases, and vice versa in passing from a carbohydrate to a proteid 

 diet. 6 



In addition to the methods of extraction already described under 

 general methods, the pancreatic enzymes may be obtained in solution by 

 various other methods, of which the following is a summary : 



1. By extracting with water saturated with chloroform; such an extract 

 keeps well and is very efficient. 7 



2. By extracting with water containing 3 to 4 per cent, of a mixture of 

 2 parts of boracic acid and 1 part of borax. 8 



3. By placing the fresh gland, finely minced, in a saturated solution of 

 sodium chloride. This gives a strong solution of the proteolytic and diastatic 

 enzymes. 9 



4. By extracting the fresh pancreas, freed from fat and finely minced, 

 with about four times its weight of 25 per cent, alcohol for four or five days; 

 succeeded by filtration, which may be assisted by a trace of acetic acid. 10 



1 For a detailed account of the action of pancreatic extracts in different animals, see 

 Harris and Gow, Journ. PhysioL, Cambridge and London. 1892, vol. xiii. p. 469. 



2 A milk curdling enzyme is also present ; see Milk, p. 127. 



3 Krukenberg, " Grundziige einer vergleichenden Physiologic der Verdauung," Heidel- 

 berg, 1882. 



4 Korowin, Jahresb. u. d. Fortschr. d. Thier-Chem., Wiesbaden, 1873, Bd. iii ; Zweifel, 

 "Untersuch. ueber den Yerdauungsapparat der Neugeborenen," Berlin, 1874. 



5 Albertoni, Jahresb. ii. d. Fortschr. d. Thier-Chem., Wiesbaden, 1878, Bd. viii. S. 254. 



6 Vassiliew, Arch, de sc. biol., St. Petersbourg, 1893, vol. ii. p. 219 ; Jahresb. it. d. 

 Fortschr. d. Thier-Chem., Wiesbaden, 1893, Bd. xxiii. S. 219. 



7 Roberts, "Lumleian Lectures," 1880 ; "Digestion and Diet," London, 1891, p. 18. 



8 Roberts, loc. cit. 



9 Roberts, loc. cit. Also recommended by Harris and Gow, Journ. PhysioL, Cambridge 

 and London, 1892, vol. xiii. p. 469. 



10 Roberts, loc. cit. 



