190 PROPERTIES OF GASTRIC JUICE. 
alimentary mass into contact with its sides, so that the whole 
is after a time equally exposed to the influence of the gastric 
secretion. If this movement were not to take place, only the 
outside of the mass would be digested, and the central rtm 
would remain but little affected. 
. 207. The nature of the gastric fluid, and the sitoile of its 
operation upon the food, have been studied by withdrawing 
a portion of it from the stomach, and by observing its pro- 
perties and actions out of the body. A sufficient quantity 
for this purpose cannot be easily procured. ‘Spallanzani, an 
- Italian physiologist of the last century, contrived to obtain 
it, by causing birds and other animals to swallow sponges to 
which pieces of thread were attached ; these, when they had 
remained long enough in the stomach to cause a secretion of 
the gastric juice, were drawn up again ; and the fluid they 
had absorbed was pressed out into vessels, in which its pro- 
perties could be examined. More recently, however, an 
advantageous opportunity has presented itself for obtaining 
supplies of gastric fluid in a less objectionable manner. A 
young man, named Alexis St. Martin, received a very severe 
wound in his left side, by the bursting of a gun; and al- 
though this wound laid open the cavity of his stomach, he 
recoyered his health completely, and subsequently married 
and had a family. There remained, however, an aperture in 
his stomach, which would not close up; and through this 
orifice, which was usually covered by a bandage, the contents 
of the stomach could be drawn out. The gastric juice was 
obtained by introducing an India-rubber tube into the sto- 
mach when it was empty, and by moving it about within the 
cavity ; the contact of the tube then excited the follicles to 
secretion (on the principle already mentioned, § 204); and 
the fluid thus poured into the stomach was drawn off geen 
the tube. 
208. The Gastric Juice is very like saliva in its appearance, 
but it is distinctly acid to the taste; and it is found, by 
chemical examination, to contain a considerable quantity of 
muriatic acid * in an uncombined state. Besides this, it con- 
tains a considerable quantity of a peculiar animal substance 
which seems like altered albumen, and which has been desig- 
nated pepsin; as well as other ingredients of less importance, 
* Muriatic acid is commonly known as spirit of salt, 
