ABSORPTION AND SANGUIFICATION. 277 



CHAPTER V. 



ABSORPTION AND SANGUIFICATION. 

 1. Absorption from the Digestive Cavity. 



189. So long as the Alimentary matter is contained in the digestive 

 cavity, it is as far from being conducive to the nutrition of the system, 

 as if it were in contact with the external surface. It is only when 

 absorbed into the vessels, and carried by the circulating current into 

 the remote portions of the body, that it really becomes useful in main- 

 taining the vigour of the system, by replacing that which has decayed, 

 and by affording the materials for the various organic processes which 

 are continually going on. Among the Invertebrated animals, we find 

 the reception of alimentary matter into the circulating system to be 

 entirely accomplished through the medium of the veins, which are dis- 

 tributed upon the walls of the digestive cavity. We not unfrequently 

 observe, that the intestinal tube is completely enclosed within a large 

 venous sinus, so that its whole external surface is bathed with blood ; 

 and into this sinus, the alimentary materials would appear to transude, 

 through the walls of the intestinal canal, to become mingled with the 

 blood, and to be conveyed with its current into the remote portions of 

 the body. Among the Vertebrata, we find an additional set of vessels, 

 interposed between the walls of the intestine and the sanguiferous sys- 

 tem, for the purpose, as it would seem, of taking up that portion of the 

 nutritive matter which is not in a state of perfect solution, and of pre- 

 paring it for being introduced into the current of the blood. These 

 vessels are the lacteah or absorbents. They are very copiously distri- 

 buted upon the walls of the small intestine, commencing near the 

 entrance of the biliary and pancreatic ducts ; the walls of the large 

 intestine are less abundantly supplied with them, and they do not show 

 themselves in the villi which are found on some parts of the lining mem- 

 brane of the stomach, although the walls of that viscus are supplied with 

 lymphatic absorbents. 



490. Nevertheless it is quite certain, that substances may pass into 

 the current of the circulation, which have been presented from passing 

 further than the stomach ; thus, if a solution of Epsom-salts be intro- 

 duced into the stomach of an animal, and its passage into the intestine 

 be prevented by a ligature around the pylorus, its purgative action 

 will be exerted nearly as soon, as if the communication between the 

 stomach and intestines had been left quite free ; or if a solution of 

 prussiate of potash be introduced into the stomach under similar 

 circumstances, the presence of that salt in the blood may be speedily 

 demonstrated by chemical tests. It appears from the experiments of 

 MM. Tiedemann and Gmelin, that when various substances were min- 

 gled with the food, which, by their colour, odour, or chemical properties 

 might be easily detected, such as gamboge, madder, rhubarb, camphor, 



