69G 
MR. J. N. LANGLEY ON THE HISTOLOGY AND 
The gland-cells do not store up pepsin as such, hut store up zymogen, out of which 
pepsin arises when the cell secretes. 
The researches of Heidenhain* have shown that the cells of the pancreas do not 
store up trypsin but store up a substance which under certain conditions can give rise 
to trypsin. 
Since it had been shown by Ebstein and GnuTZNEid that the gastric glands of 
Mammals contain a certain quantity of a substance capable, when acted on by sodium 
chloride or by dilute hydrochloric acid, of giving rise to pepsin, Heidenhain introduced 
the word “zymogen” to include the antecedent of the ferment in both these and in 
any later found cases. 
In the pancreas the conspicuous granules in the cells consist in part or wholly of 
zymogen. The zymogen can then in this instance be distinguished from the rest of 
the cell-substance. 
When we compare in the Frog the pancreatic with the oesophageal gland-cells, and 
observe the close resemblance which exists between the two, especially as regards the 
granules they contain, it seems in the highest degree improbable that they should 
differ so widely as that one should store up zymogen and the other store up ferment. 
We have seen that the gastric glands of the Newt closely resemble the oesophageal 
glands of the Frog as regards the reaction and behaviour of the granules they contain : 
the other gastric glands we have investigated above, differ in some points from both 
of these glands, but in the important point of the behaviour of their granules show a 
general similarity to them. In these glands then, too, the microscopical appearances 
seem to me to render it far more probable that the granules stored up should consist 
of zymogen, than that they should consist of ferment or other ready-formed secretory 
product. 
I know of no satisfactory instance in any gland in which the substances found in the 
secretion are found stored up in the cells. In the liver-cells none of the characteristic 
constituents of bile are found. It may be objected that in these no substance is 
stored up, and that the cell protoplasm in activity forms straightway and excretes the 
constituents of bile. From many observations carried on during the past twelve 
months on the liver of the Frog, Toad, Newt, and Snake, I have been able to satisfy 
myself that in these cases also granules are stored to be used during secretion. 
In mucous glands the evidence is against the substance stored by the cells being 
actually the mucin found in the fluid secreted. It is probably a pre-product closely 
related to mucin. 
In the serous glands the facts known are not sufficient to be of much use for or 
against. 
* Heidenhain, Pfluger’s Arcliiv., Bd. x., s. 557, 1875. 
t Ebstein and Gbutzner, Pfluger’s Archiv., Bd. viii., s. 122, 1874. 
