164 FUNCTIONS OF NUTRITION. 



the whole is reduced to a uniform mixture, of gruelly consistency, in 

 which only remnants of the muscular fibres can be detected by the 

 microscope. It is this apparently homogeneous, pultaceous, or semi-fluid 

 material that was formerly designated by the name of " chyme." It is 

 a mixture of disintegrated and semi-digested tissues, portions of which 

 have been liquefied while others are not yet reduced to a state of 

 solution. 



Milk, when taken into the stomach in a fresh condition, is first coagu- 

 lated, afterward dissolved. The preliminary coagulation of its caseine, 

 under the influence of the gastric juice, takes place very rapidly. 

 Beaumont found that milk could be withdrawn in a coagulated condi- 

 tion fifteen minutes after its introduction into the stomach ; and that 

 if the mixture were kept at the temperature of 38 C., the coagula were 

 again liquefied in the course of eight hours The coagulation of milk, 

 by contact with the gastric juice, is in the form of minute, soft flocculi, 

 which, at the temperature of the body, readily undergo the conversion 

 into peptone, and are thus redissolved. Milk, as used by adults, in 

 various culinary preparations, is generally incorporated, in the coagu- 

 lated form, with other articles of food. 



The vegetable tissues, as a rule, are digested in a manner similar to 

 that described above. The albuminous matters are dissolved out, leav- 

 ing the starchy and oleaginous ingredients in a free condition, but chemi- 

 cally unchanged. As these tissues generally contain a smaller propor- 

 tion of albuminous matter than animal food, the main result of the 

 changes which they undergo in the stomach is their disintegration. 



The gastric juice, after commencing its action in the stomach, passes, 

 with the debris of the food, into the intestine. This can be seen in the 

 dog by killing the animal after feeding, and examining the contents of 

 the alimentary canal. The same thing may be observed by means of 

 a duodenal fistula, established by an operation similar to that for fistula 

 of the stomach. A silver tube, with flanges at each end, is introduced 

 into the lower part of the duodenum, and the wound allowed to heal, 

 after which the contents of the intestine may be withdrawn and exam- 

 ined at different periods of digestion. 



About half an hour after the ingestion of a meal, the gastric juice 

 begins to pass into the duodenum, recognizable by its strongly-marked 

 acidity, and containing a certain quantity of peptone in solution. It 

 soon afterward becomes mingled with the debris of muscular fibres, fat 

 vesicles, and oil drops ; substances easily recognizable under the micro- 

 scope, and which produce a grayish turbidity in the fluid withdrawn 

 from the fistula. By the continuous passage, in this way, of alimen- 

 tary material, mixed with gastric juice, the stomach becomes gradually 

 cleared of its contents. In the experiments of Beaumont the time 

 required for the disappearance of food from the stomach varied from 

 one hour to five hours and a half, according to the quality and quantity 

 of the material used. In those of Prof. F. G. Smith on the same sub- 

 ject, food seldom remained in the stomach more than two hours after its 



