336 CHEMISTR 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 l 
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 versd 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, Jalircsb. it. d. Furlschr. d. Thier-Clicm., Wiesbaden, 1873, Bd. iii ; Zvveifel, 
" Untersuch. ueber den Verdauungsapparat der Neugeborenen," Berlin, 1874. 
5 Albertoni, Jahresb. il. d. Fortschr. d. Tkier-Chem., Wiesbaden, 1878, Bd. viii. S. 254. 
6 Vassiliew, Arch, da sc. biol., St. Petersbourg, 1893, vol. ii. p. 219 ; Jahresb. it. d. 
Fortschr. d. Thicr-Chem., Wiesbaden, 1893, Bd. xxiii. S. 219. 
7 Roberts, " Lumleian Lectures," 1880 ; "Digestion and Diet," London, 1891, p. IS. 
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. 
