INFLUENCE OF ENDOSMOSIS AND TEANSUDATION. 



action, in the same way that the exposed membranes of an 

 egg may be ruptured by endosmosis, when immersed in 

 water. 



We have already alluded to the influence of transudation 

 from the blood-vessels, and compared it to the force with which 

 the secretions are discharged into the ducts of the glands ; and 

 in placing this, with the force of endosmosis, at the head of the 

 list of the agents which effect the lymphatic circulation, its 

 importance is not over-estimated. This conclusion can hardly 

 be avoided, when we consider the anatomy of the lymphatic 

 system. The situations in which the endosmotic force ori- 

 ginates are at the periphery, where the single homogeneous 

 wall of the plexus is excessively thin, and the extent of 

 absorbing surface is enormous. If liquids can penetrate with 

 such rapidity and force through the walls of the blood-ves- 

 sels, where their entrance is opposed by the pressure of the 

 fluids already in their interior, they certainly must pass with- 

 out difficulty through the walls of the lymphatics, where 

 there is no lateral pressure to oppose their entrance, except 

 that produced by the weight of the column of liquid. This 

 pressure is readily overcome ; and the numerous valves in 

 the lymphatic system effectually prevent any backward cur- 

 rent. Every particle of liquid that passes into the lymphat- 

 ics by endosmosis or by transudation, produces movement by 

 displacing an equal bulk of liquid contained in the vessel. 

 We observe with the microscope the rapid filling and rup- 

 ture of microscopic cells when immersed in water ; and the 

 rough experiments by which the operation of endosmosis is 

 ordinarily illustrated, in which the extent of endosmotic sur- 

 face is infinitely small compared with the lymphatic system, 

 exhibit a current of considerable force and rapidity. When 

 we remember that the infinitely numerous lymphatic radi- 

 cles are bathed in fluids, which undoubtedly pass into their 

 interior with great facility, and compare the probable extent 

 of this endosmotic surface with the diameter of the thoracic 

 duct, we can hardly be surprised that this force should be ca- 



