INFLUENCE OF THE NERVOUS SYSTEM ON ABSORPTION 255 



it has been ascertained that the epithelium plays an important part in 

 this process.' During the digestion of fat, these cells become filled 

 with fatty granules. It has not been demonstrated precisely how fatty 

 particles penetrate the epithelium, but the fact can not be doubted. 

 From the epithelium, the particles of emulsion pass into the substance 

 of the villi probably into the lymph-spaces and canals and from 

 these they readily find their way into the lymphatic capillaries. It has 

 been shown that fatty emulsion will pass more easily through porous 

 septa that have been moistened with bile ; and it is probably in this 

 way mainly that the bile aids in the passage of the fine particles of fat 

 into the lacteals. 



As a rule, insoluble substances, with the exception of the fats, are 

 never regularly absorbed, no matter how finely they may be divided. 

 The apparent exceptions to this are mercury in a state of minute sub- 

 division like an emulsion, and carbonaceous particles. As regards mer- 

 cury, it is well known that minute particles in the form of unguents 

 may be introduced into the system by prolonged frictions ; but this can 

 not be taken as an instance of physiological absorption. The passage 

 of small carbonaceous particles through the pulmonary membrane 

 seems to be purely mechanical. The same thing possibly may occur 

 when fine sharp particles of carbon are introduced into the alimentary 

 canal. 



Influence of the Condition of the Blood and of the Vessels on Absorp- 

 tion. After loss of blood or its deterioration and concentration from 

 prolonged abstinence, absorption^ takes place with great activity. This 

 is well known, both as regards the entrance of water and alimentary 

 substances and the absorption of drugs. It was at one time quite a 

 common practice to bleed before administering certain remedies, in order 

 to produce a more speedy action. 



The rapidity of the circulation has an important influence in facilitat- 

 ing absorption ; and this process usually is active in proportion to the 

 vascularity of different parts. During intestinal absorption, the increase 

 in the activity of the circulation in the mucous membrane is very marked 

 and undoubtedly has an influence on the rapidity with which the prod- 

 ucts of digestion are taken up. 



Influence of the Nervous System on Absorption. It is certain that 

 absorption, especially in the stomach, is subject to certain variations 

 which can hardly be dependent on anything but nervous action. Liquids 

 that usually are readily absorbed from the stomach are sometimes retained 

 for a time and are afterward rejected in nearly the condition in which 

 they were taken. It is probable, however, that the most important influ- 

 ences thus exerted by the nervous system are effected through the circu- 



