464 ABSORPTION. 



case of mercury, it is well known that minute particles in 

 the form of unguents may be introduced into the system by 

 prolonged frictions ; but this cannot be regarded as an in- 

 stance of physiological absorption. - We have already con- 

 sidered the subject of the passage of small carbonaceous 

 particles through the pulmonary membrane, and have seen 

 that their penetration is purely mechanical. 1 The same thing 

 may possibly occur when fine sharp particles of carbon are 

 introduced into the alimentary canal ; but the experiments 

 of Mialhe with pulverized charcoal, 2 and particularly those 

 those of Berard, Robin, and Bernard with lamp-black intro- 

 duced into the intestinal canal of animals, showed that 

 though the intestinal mucous membrane became of a deep 

 black, this could easily be removed by a stream of water, 

 and no carbonaceous particles could be discovered in the 

 mesenteric veins, the lacteals, or the mesenteric glands. 3 

 When the carbon is used in the form of lamp-black, the 

 particles are very minute and rounded, and do not present 

 the sharp points and edges which sometimes enable the 

 grains of pulverized charcoal to penetrate the vessels me- 

 chanically. 



Variations and Modifications of Absorption. 



Yery little is known concerning the variations in lacteal 

 or lymphatic absorption ; but in absorption by blood-vessels, 

 important modifications occur, due, on the one hand, to dif- 

 ferent conditions of the fluids to be absorbed, and on the 

 other, to differences in the constitution of the blood and in 

 the conditions of the vessels. 



The different conditions of the fluids to be absorbed ap- 

 parently do not always have the same influence in physio- 

 logical absorption as in endosmotic experiments made out 

 of the body. Saccharine solutions of different densities con- 



1 Yol. i., Kespiration, p. 364. 



2 MIALHE, Ghimie appliquee d la Physiologic, Paris, 1856, p. 197. 

 8 BEKARD, Cours de Physiologic, Paris, 1849, tome ii., p. 729. 



