314 ABSORPTION. 



in the quantity of blood coming from the intestine and the rapidity of its circulation, as 

 compared with the chyle, will explain the more rapid penetration by endosmosis of the 

 soluble products of digestion. 



Absorption of Water ~by the Lacteals. There can be no doubt that a small portion of 

 the liquids taken as drink finds its way into the circulation by the lacteals, although the 

 greatest part passes directly into the blood-vessels. This has been proven by experi- 

 ments of a most positive character. Leuret and Lassaigne state that, when an animal is 

 fed with an aliment which is very substantial and is killed during digestion, the thoracic 

 duct contains a very small quantity of chyle ; but, when the animal has taken liquids with 

 the food, the thoracic duct and the lacteals are very much distended. In an experiment 

 by Ernest Burdach, a dog was deprived of food and drink for twenty-four hours, after 

 which he was allowed to drink water, and, in addition, half a pound was injected into 

 the stomach. The animal was killed a half an hour after, and the thoracic duct was 

 found engorged with watery lymph, which contained a very small number of lymph-cor- 

 puscles. 



In discussing the question of absorption by the blood-vessels of the intestinal canal, 

 we alluded to experiments which showed that various poisonous substances introduced 

 into the intestines produced their characteristic effects upon the system with great 

 rapidity when the veins leading from the part were intact, while no such effects followed 

 when the only avenue to the general system was through the lacteals. Without again 

 discussing these observations in detail, it may be stated, as the general results of experi- 

 ments on this subject, that few, if any, of the active poisons were found to be absorbed 

 from the alimentary canal, except by blood-vessels ; and, when soluble coloring matters, 

 or salts which could be easily recognized, were found in the lacteals or the thoracic duct 

 after they had been introduced into the intestine, they penetrated in small quantity and 

 very slowly ; while it has been repeatedly found that the same substances were taken up 

 by the veins with great rapidity and excreted, in many instances, by the urine. 



Absorption from Parts not connected with the Digestive System. Aside from the 

 entrance of gases into the blood from the pulmonary surface, physiological absorption is 

 almost entirely confined to the mucous membrane of the alimentary canal. It is true 

 that liquids may find their way into the circulation through the skin, the lining mem- 

 brane of the air-passages, the reservoirs, ducts, and parenchyma of glands, the serous and 

 other closed cavities, the areolar tissue, the conjunctiva, the muscular tissue, and, in 

 fact, all parts which are supplied with blood-vessels ; but here the absorption of foreign 

 matters is an occasional or an accidental circumstance and is not connected with the 

 general process of nutrition. It is now well known that all parts of the body, except 

 the epidermis and its appendages, the epithelium, and some other structures which are 

 regularly desquamated, are constantly undergoing change, and the effete matters which 

 result from their decay are taken up by what is called interstitial absorption and are car- 

 ried by the blood to the proper organs, to be excreted. It seems probable that the ves- 

 sels of these parts would also be capable of taking up soluble foreign substances when 

 presented to them ; and this is, indeed, the fact with regard to all parts in which the 

 nutritive processes are even moderately active, or where the structures covering the vas- 

 cular parts are permeable. 



Absorption from the Skin. It is now generally admitted that absorption can take 

 place from the general surface, although, at one time, this was a question much discussed 

 by physiologists and practical physicians. The proofs, however, of the entrance of cer- 

 tain medicinal preparations from the surface of the body are now entirely conclusive ; 

 and the constitutional effects of medicines administered in this way are frequently as 

 marked as when they are taken into the alimentary canal. But the question which is 



