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 portion 

 would remain but little affected. 



207. The nature of the gastric fluid, and the mode 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 

 recovered 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 through 

 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. 



