ABSORPTION BY THE RESPIRATORY SURFACE 253 



vessels, a small quantity is also absorbed by the lacteals. In the com- 

 parative analyses of the chyle and lymph by Rees, the proportion of 

 inorganic salts was found to be considerably greater in the chyle. The 

 great excess in the quantity of blood coming from the intestine, and the 

 rapidity of its circulation, as compared with the chyle, explain the more 

 rapid penetration by osmosis 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 circula- 

 tion by the lacteals, although the greatest part passes directly into the 

 bloodvessels. When an animal has taken solid food only and is killed 

 during digestion, the thoracic duct contains but a small quantity of chyle ; 

 but when the animal has taken liquids with the food, the thoracic duct 

 and the lacteals are distended. 



Aside from the entrance of gases into the blood from the pulmonary 

 surface, physiological absorption is confined almost entirely to the mu- 

 cous membrane of the alimentary canal. It is true that liquids may find 

 their way into the circulation through the skin, the lining membrane of 

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

 and other closed cavities, areolar tissue, the conjunctiva, muscular tis- 

 sue, and, in fact, all parts that are supplied with bloodvessels ; but 

 here the absorption of foreign matters is occasional or accidental and 

 is not connected with general nutrition. 



Absorption by the Skin. It is now admitted that absorption may take 

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

 much discussed by physiologists. The proofs, however, of the entrance 

 of certain medicinal preparations from the surface of the body are con- 

 clusive. The question of most importance in this connection relates to 

 the normal action of the skin as an absorbing surface. Looking at this 

 subject from a purely physiological point of view, absorption from the 

 skin, under ordinary conditions, must be very slight, if, indeed, it takes 

 place at all. There are, nevertheless, facts that render it certain that 

 water may be absorbed by the skin and relieve in some degree the sen- 

 sation of thirst. 



Absorption by the Respiratory Surface. Animal and vegetable 

 emanations may be taken into the blood by the lungs and produce 

 well-marked pathological conditions. Many contagious diseases are 

 propagated in this way, as well as some fevers and other general 

 diseases that are not contagious. In regard to certain poisonous gases 

 and volatile matters, the effects of their absorption by the lungs are 

 even more striking. Carbon monoxide and arsine produce death 

 almost instantly, even when inhaled in very small quantity. The 

 vapor of pure hydrocyanic acid acts frequently with great promptness 



