DIGESTION AND FOOD, 39 



CHAPTER VIII. 



Chyme. Intestinal Canal. Mucous Membrane. Lacteals. 

 Chyme in the Duodenum. Chyle : differs with difference of 

 Food. Carried to Blood-Vessels. Three Stages of Digestion. 



63. "When the stomach has finished its work, the food is 

 converted into chyme. To the naked eye, it is the same in 

 appearance throughout. All distinctions of the various 

 kinds of aliment seem to be lost. No traces of the meats, 

 bread, or vegetables are visible ; all are reduced to an ap- 

 parently homogeneous pulp. These were the former no- 

 tions of science. But modern microscopic investigations 

 and chemical analyses show that this is not homogeneous ; of 

 this a part only is digested, or converted to chyme ; the rest, 

 though finely divided and mixed with the fluids of the stom- 

 ach, is yet to be submitted to a farther process of digestion 

 in the small intestines. When the stomach has finished its 

 work on the food, the pyloric valve opens, the muscular 

 coal contracts, and, pressing upon the contents, forces this 

 pulp through this passage into the duodenum, (Fig. IV. c, c,) 

 which is the next link in the alimentary canal. 



69. The intestinal canal is composed of three coats, 

 which are similarly arranged and serve similar purposes to 

 those of the stomach. The outer of these coats is strong 

 and thick, and gives support to the whole canal ; by this coat 

 the organ is attached to the back-bone and held in its place. 

 The middle coat is like the lean meat of tripe ; it is com- 

 posed of two sets or layers of fibres, one of which winds 

 around the tube the other runs lengthwise from end to 

 end. The circular band regulates the size of the tube, by 

 keeping it always pressed down upon its contents. When food 

 is within this organ, these fibres contract, one after another, 

 successively, and, pressing upon the matters contained within, 

 force them onward. The longitudinal fibres shorten the 



