228 DIGESTION. 



circumstances, from three to four hours may be taken as the 

 average time occupied by the digestion of a meal in the stom- 

 ach. 



Dr. Beaumont constructed a table showing the times required 

 for the digestion of all usual articles of food in St. Martin's 

 stomach, and in his gastric fluid taken from the stomach. 

 Among the substances most quickly digested were rice and 

 tripe, both of which were chymified in an hour; eggs, salmon, 

 trout, apples, and venison, were digested in an hour and a half; 

 tapioca, barley, milk, liver, fish, in two hours; turkey, lamb, 

 potatoes, pig, in two hours and a half; beef and mutton re- 

 quired from three hours to three and a half, and both were 

 more digestible than veal ; fowls were like mutton in their de- 

 gree of digestibility. Animal substances were, in general, con- 

 verted into chyme more rapidly than vegetables. 



Dr. Beaumont's experiments were all made on ordinary arti- 

 cles of food. A minuter examination of the changes produced 

 by gastric digestion on various tissues has been made by Dr. 

 Rawitz, who examined microscopically the product of the arti- 

 ficial digestion of different kinds of food, and the contents of 

 the faeces after eating the same kinds of food. The general 

 results of his examinations, as regards animal food, show that 

 muscular tissue breaks up into its constituent fasciculi, and 

 that these again are divided transversely; gradually the trans- 

 verse strife become indistinct, and then disappear; and finally, 

 the sarcolemma seems to be dissolved, and no trace of the tissue 

 can be found in the chyme, except a few fragments of fibres. 

 These changes ensue most rapidly in the flesh of fish and hares, 

 less rapidly in that of poultry and other animals. The cells of 

 cartilage and fibro-cartilage, except those of fish, pass unchanged 

 through the stomach and intestines, and may be found in the 

 faeces. The interstitial tissues of these structures are converted 

 into pulpy textureless substances in the artificial digestive fluid, 

 and are not discoverable in the faeces. Elastic fibres are un- 

 changed in the digestive fluid. Fat-cells are sometimes found 

 quite unaltered in the faeces; and crystals of cholesterin may 

 usually be obtained from faeces, especially after the use of pork 

 fat. 



As regards vegetable substances, Dr. Rawitz states, that he 

 frequently found large quantities of cell-membranes unchanged 

 in the faeces ; also starch-cells, commonly deprived of only part 

 of their contents. The green coloring principle, chlorophyll, 

 was usually unchanged. The walls of the sap-vessels and 

 spiral-vessels were quite unaltered by the digestive fluid, and 

 were usually found in large quantities in the faeces; their con- 

 tents, probably, were removed. 



