DIGESTION. 1G3 



that which is near its termination in the intestine. 

 At the pylorus itself, the diameter of the passage is 

 much constricted, by a fold of the inner membrane, 

 which is surrounded by a circular band of mus- 

 cular fibres, performing the office of a sphincter, 

 and completely closing the lower orifice of the 

 stomach, during the digestion of its contents. 



The principal agent in digestion, as far as the 

 ordinary chemical means are concerned in that 

 operation, is a fluid secreted by the coats of the 

 stomach, and termed the Gastric juice. This fluid 

 has, in each animal, the remarkable property of 

 dissolving, or at least reducing to a pulp, all the 

 substances which constitute the natural food of that 

 particular species of animal; while it has compara- 

 tively but little solvent power over other kinds of 

 food. Such is the conclusion which has been 

 deduced from the extensive researches on this 

 subject made by that indefatigable experimentalist, 

 Spallanzani, who found in numberless trials that 

 the gastric juice taken from the stomach, and put 

 into glass vessels, produced, if kept at the usual 

 temperature of the animal, changes to all appear- 

 ance exactly similar to those which take place in 

 natural digestion.* In animals which feed on flesh, 



* The accuracy of this conclusion has been lately contested by 

 M. de Montegre, whose report of the effects of the gastric juice of 

 animals out of the body, does not accord with that of Spallanzani ; 

 but the difference of circumstances in which his experiments were 

 made, is quite sufficient to account for the discrepancy in the results; 

 and those of M. De Montegre, therefore, by no means invalidate the 

 general facts stated in the text, which have been established by the 

 experiments, not only of Spallanzani, but also of Reaumur, Stevens, 

 Leuret, and Lassaigne. See Alison's Outlines of Physiology and 

 Pathology, p. 1 70. 



