/•( )RMATION OF FERMENTS OE GASTRIC J I 'ICE. 543 
pepsin, but would yield the same under appropriate treatment. The 
differentiation of the one from the other was further advanced by 
Langley and Kdkins. 1 They confirmed the observation, that alkalies 
and alkaline Baits rapidly destroy pepsin. The conditions influencing 
the rate of destruction by sodium carbonate were found to he the 
strength of the solution of the alkaline salt, the time during which it is 
allowed to act, the temperature of the mixture, and finally the amount 
of proteids present. By mere neutralisation of an acid solution of 
pepsin, a considerable amount might he destroyed. If equal volumes of 
an extract of pepsin and of a 1 per cent, solution of sodium carbonate 
were mixed, in fifteen seconds as much as 97 per cent, of the pepsin 
might be destroyed. The greater the amount of proteid present, the 
greater the amount of sodium carbonate necessary to cause destruction. 
The difference between pepsin and pepsinogen in their behaviour with 
different reagents is merely one of degree. Pepsinogen is destroyed 
also by alkalies, but the destruction is so slow as compared with that of 
pepsin, that this reaction furnishes a useful method of distinguishing 
the one from the other. Since the aqueous extract of the gastric 
mucous membrane of a fasting animal loses but very little peptic 
power on brief treatment with 1 per cent, sodium carbonate, it follows 
that pepsinogen, but little or no pepsin, is present in the gastric glands 
in hunger. Schiff stated that " propepsin " was slowly converted into 
true pepsin. Langley and Edkins found that the conversion of 
pepsinogen into pepsin is one of great rapidity. All the pepsinogen 
present in an aqueous extract of a cat's gastric mucous membrane 
may be converted into pepsin by treatment with 1 per cent, hydro- 
chloric acid in sixty seconds. With reference to the point as to 
whether pepsin is present in the gland cells during digestion, no definite 
result was arrived at. Pepsin can be obtained from the gastric 
mucous membrane of an animal in digestion, but not invariably, and 
Buch as is found may have been produced by the acid in the lumen of 
the tubes affecting the pepsinogen in the contiguous chief cells. In the 
oesophagus of the frog, where no acid is secreted, but only ferment, 
injection of commercial peptone causes no accumulation of pepsin in 
the gland cells. Carbonic acid destroys pepsinogen more rapidly than 
pepsin : but if only a small quantity of peptone is present, there is 
practically no destruction. Finally, it is observed that both pepsin and 
pepsinogen are rapidly destroyed on heating to a temperature of 55°- 
0/ L. 
(b) The conditions of formation of rennin (rennet-fernn nt). — An enzyme 
which has the property of causing milk or the separated caseinogen 
to undergo coagulation, is found in the stomachs of almost all animals. 
As regards the secretion of rennin, there is an important resemblance 
to that of pepsin, inasmuch as, in the case of the former, there is a 
precursor of the actual ferment existent in the glands of the stomach 
which has the power, under the influence of acid, of producing the 
active enzyme. It was in the case of the rennin that it first was 
shown that many of the ferments of the alimentary canal have a 
zymogen stage. Hammarsten,' 2 in 1872, pointed out that the gastric 
glands of manv animals contain rennet-zvmoo-en, but do not contain 
rennet-ferment. The zymogens of pepsin and trypsin were not 
1 " Pepsin and Pepsinogen," Jouru. Physiol., Cambridge and London, 1886, vol. vii. 
2 Jahresb. ii. d. Fortschr. d. Thier-Chem., Wiesbaden, 137:2. 
