338 
PEPSINE. 
By the term gastric juice is understood a fluid secreted 
by the stomach, and poured into it through a number of 
minute tubes, situated in the mucous membrane which forms 
the interior coat. These tubes are, during fasting, plugged 
up by a mass of epithelial cells ; but when the mucous mem- 
brane is irritated by food or by certain other stimulants — 
pepper, for example — the secretion of gastric juice com- 
mences, the plugs of epithelium are expelled, and the juice 
distils into the cavity of the stomach. 
Gastric juice contains about 97 per cent, water, ]*25 per 
cent, pepsine, and T7<5 per cent, salts, consisting of carbonate 
and phosphate of lime, chloride of sodium, minute traces of 
sulphates, and sometimes a trace of ammoniacal salts. The 
proportions, however, in which these inorganic constituents 
are present, vary considerably. Lastly, the gastric juice 
contains a free acid, which is one of the most important 
components. 
As it would be impossible to obtain a sufficient quantity of 
gastric juice for medicinal purposes from living animals, 
either by fistulous openings or any other method, we seek to 
intercept the pepsine before it passes into the stomach, and 
to extract it from the little tubes in w hich it is secreted or at 
all events along which it passes on its way. For this purpose 
the rennet-bags of sheep are the most convenient, on account 
of the large supply which is always at hand ; and the fol- 
lowing process has been proposed by M. Boudault : — The 
rennet-bags are opened and reversed, and w ? ashed under a 
thin stream of w r ater, to free them from alimentary matters, 
&c. The mucous membrane is then carefully scraped off 
with a knife, the cells are bruised in a mortar, and digested 
for twelve hours in distilled water. The liquid is then fil- 
tered, and neutral acetate of lead is added, which precipitates 
peptate of lead. This precipitate is collected and decomposed 
by means of sulphuretted hydrogen, pepsine is thus liberated 
in solution, and is separated from the insoluble sulphide of 
lead by filtration. This liquid represents a neutral gastric 
juice. If is, however, necessary that it should be acid, and 
for this purpose lactic acid is added until the liquid exhibits 
the same degree of acidity as a specimen of gastric juice 
obtained from the stomach of a dog by means of a fistulous 
opening. The reason why lactic acid is selected for this 
purpose will be showrn below. If the artificial gastric juice 
thus obtained, be evaporated to dryness at a gentle tem- 
perature (it should not exceed 100° Fall.), a gummy mass is 
obtained, which attracts moisture from the air, and is alto- 
gether a very unfit article either for sale or administration. 
