on the Proteolytic Action of Pepsin-hydrochloric Acid. 163 
more than four-fifths as active as 0°1 per cent. hydrochloric acid, 
while sulphuric acid is only a little more than one-fourth as active as 
the hydrochloric acid; acetic acid being practically worthless. 
Henee it is obvious, that, the base being the same, acetates, borates 
and other salts, the acids of which are not capable of working with 
pepsin, will most readily retard gastric digestion; then of the other 
salts experimented with, sulphates and lastly nitrates. 
A glance at the table of comparisons, shows here and there, results 
which manifestly accord with this view, notably lead acetate, cupric 
sulphate, zine sulphate,* magnesium sulphate and potassium nitrate. 
That this withdrawal of free hydrochloric from the pepsin, is 
only a partial explanation of the mode of action of neutral salts is 
plain from the fact that chlorides exert very pronounced retarding 
actions moreover the action of these latter as well as of the others 
cannot be due merely to mechanical causes, viz: the semi-saturation 
of the digestive fluid, since 3-0 per cent. of boracic acid stimulates 
instead of retarding, and even the presence of 10 per cent. of arsenic 
acid causes retardation amounting to only 32 per cent. According 
to Petit,t moreover, saccharose to the extent of 16 per cent. does not 
interrupt gastric digestion. Again, that the base entering into the 
composition of the salt has much to do, in many cases, with its re- 
tarding proteolytic action, is apparent when we compare the action 
of ferric chloride, manganous chloride, sodium chloride, mercuric 
chloride and other metallic salts. That this action is due in part to 
capability of combining with the proteid matter, thus rendering it 
non-digestible, is unquestionable. 
Acceleration, produced by neutral salts has been noticed by other 
observers, but no explanation of the cause has been offered. It seems 
probable, however, that in the case of pepsin-hydrochloric acid, one 
plausible reason, at least, may be suggested. If, as has been mentioned, 
many of the neutral salts are decomposed by the acid of the gastric 
juice, it would follow that the addition of very small amounts of the 
salts would diminish slightly the percentage of free hydrochloric 
acid, while the acid liberated from the salt, would be entirely without 
deleterious action. Nearly every experimenter in this direction has 
employed in the preparation of gastric juice 0°2 per cent. hydrochloric 
acid, which is well adapted for the purpose, but the action of the acid 
is dependent in part on the amount of ferment. With our solution of 
pepsin, the following results, expressed in the percentage of fibrin 
* Compare Petit, Jahresbericht fiir Thierchemie, 1880, p. 309. 
{ Jahresbericht fur Thierchemie, 1880, p. 309. 
