. 



154 DIGESTION. 



! 



becomes incorporated with the fluids of the mouth, particu- 

 larly that poured out by the parotid glands, and entangles a 

 considerable quantity of air. This preparation is important 

 in insuring the prompt and efficient action of the gastric juice. 

 It is less essential in the digestion of animal than of vegeta- 

 ble food, but still increases the facility of digestion of both. 

 Many of the vegetable grains which are covered with a hard 

 epidermis, when they escape the action of the teeth, are apt 

 to pass through the alimentary canal unchanged, and may be 

 recognized entire in the fseces. This fact with regard to the 

 digestion of vegetable grains was proven, early in the history 

 of the physiology of digestion, by the experiments of Spal- 

 lanzani, who forced fowls and rooks to swallow small, per- 

 forated metallic tubes filled with beans and grains of wheat. 

 When the grains were enclosed in these tubes entire, he 

 found them but slightly swollen and softened after a number 

 of hours' sojourn in the stomach ; but when the grains were 

 introduced slightly broken, they were found, in one experi- 

 ment, to lose one-fourth of their weight in eight hours, and 

 were at last entirely dissolved. 1 This fact was further con- 

 firmed by experiments on sheep, in which a number of tubes, 

 some filled with herbs entire, and others with herbs which 

 had been triturated, were introduced into the alimentary canal. 

 At the end of thirty-three hours, five tubes were discharged 

 by the anus. In two of these, in which the food had been 

 introduced entire, the contents were apparently unchanged, 

 but in the others, in which the food had been triturated, 

 nothing remained but a small amount of indigestible matter. 3 



1 SPALLANZANI, Opuscules de Physique, Animate et Vegetale, Pavie, 1787, tome 

 ii., p. 462. 



2 Ibid., p. 552. 



