7819.] and on the Blood in general. 273 
fluid, secreted by the stomach, and denominated the gastric 
juice, the properties of which will be first briefly considered. 
From want of proper attention being paid to the heteroge- 
neous nature of the fluids found in the stomachs of animals, 
reat confusion has arisen in the description of their, properties. 
Fordyce indeed long ago pointed out the necessity of attending 
to this circumstance, but many of his successors have not much. 
profited by his observations. The fluids of the stomach may be 
considered as arising from at least four different sources, each of 
which furnishes a distinctly different fluid. These are the sali- 
vary glands, the mucous coat and exhalents of the stomach 
itself and the passages leading to it, and lastly, the gastric 
glands, which alone indeed seem to furnish the true gastric 
juice or fluid, which appears to perform so important an office in 
the function of digestion. The saliva of different animals. of 
course must be very different. That. of man, according to Ber- 
zelius, contains, like most other products secreted by glands, no 
albumen, but a peculiar animal matter, some mucus derived 
from the mucous membrane of the mouth, &c. and the usual 
salts of the blood, all dissolved, or rather, perhaps, suspended in 
much water. The mucus derived from the mucous membrane 
of the stomach appears to resemble closely that of the mouth 
and pharynx. The fluid separated by the exhalents appears to 
consist, like that fluid in general, of little more than water hold- 
ing in solution the salts of the blood. The properties of the. 
fluid secreted by the gastric glands are unknown, it never having 
‘been obtained in a separate state. Its characteristic property 
in all animals seems to be that of coagulating milk.* These 
different fluids then, with often a portion of bile, are always 
found mixed together in the stomachs of animals, and of course 
at different times in very different proportions. Thus from the 
stomach of a dog I have sometimes obtained a limpid and 
nearly transparent fluid, incapable of coagulating milk when 
assisted by es most favourable circumstances, and apparently 
. consisting of little more than water. At other times I have 
obtained a fluid capable of coagulating milk very readily. 
A question strongly agitated among physiologists has been, 
‘whether the fluids of the stomach are naturally acid or alkaline. 
Spallanzani maintained that they are naturally neutral, and this 
Opinion appears to be most probable ; though the contents of the 
stomach, when the digestive process is going on, are almost 
always acid. The nature of this acid I have not been able to 
‘ascertain in a satisfactory manner. By some of the older che- 
mists, it was asserted to be the phosphoric. M. Montegre 
Says, itis the acetic.+ It is evidently some volatile acid, from 
* Sce experiments to ascertain the coagulating power of the secretion of the 
pastric glands. “By Sir EL, Home. Phil. Trans, 1813. Part 1. 
} Seeashort acconut of the experiments of M, -Montegrevin the report of the 
Moya) Institute of France, for 1812. 
