502 ABSORPTION. 



they exist in the living organism. The vast extent of the 

 absorbing surfaces ; the great delicacy and permeability of 

 the membranes ; the rapidity with which principles are car- 

 ried on by the torrent of the circulation, as soon as they pass 

 through these membranes ; the uniformity of the pressure, 

 notwithstanding the penetration of liquids; all these favor 

 the physical phenomena of absorption in a way which can- 

 not be imitated in artificially constructed apparatus. It 

 is not necessary to invoke the vital properties of tissues to 

 explain the ordinary phenomena of absorption. Enough has 

 been learned of the laws which regulated endosmosis and 

 exosmosis to enable us to explain most of these phenomena 

 upon physical principles. This fact has been apparent in 

 studying these principles in their relation to absorption in 

 the living body- But it is an important question to deter- 

 mine whether this be applicable to all the varied phenomena 

 of physiological absorption. In other words, are there any 

 modifications in this function which cannot, as yet, be ex- 

 plained by physical laws ? 



Admitting the fact that the general process of absorption 

 takes place in accordance with the laws of endosmosis, we 

 will now consider some of the phenomena which appear to 

 be in opposition to known physical principles, or in which 

 the application of these principles seems to be imperfectly 

 understood. 



It is not easy to understand how particles of emulsified 

 fat find their way through the walls of the lacteals and the 

 blood-vessels. The experiments of Matteucci with alkaline 

 emulsions, which we referred to fully in connection with the 

 absorption of fats, seem to show that alkalinity is a condition 

 necessary to the penetration of fatty particles, though they do 

 not offer an explanation of the mechanism by which these 

 particles pass through membranes. It has been demonstrated 

 that the epithelium which covers these membranes becomes 

 filled with fatty granules during the absorption of emulsions, 

 and we must invoke the aid of " cell-action," concerning 



