54 ENDOSMOSE. PEKMEABILITY TO GASES. [CHAP. I. 



reach the top and flow over. " The first moving power here," says 

 Professor Daniell, " is the force of adhesion between the water and 

 the bladder; the former penetrates the pores of the latter, and 

 comes in contact, upon its npper surface, with the spirit, by the 

 attraction of which, it is removed from the bladder and mixes with 

 its mass. The height of the column is in some degree the mea- 

 sure of the force thus called into action." The purely physical 

 nature of this process is shewn by the fact that it will equally 

 take place through porous inorganic substances, as through organic 

 membranes. It would be impossible to do more here than give a 

 brief explanation of this remarkable phenomenon. It is important 

 to add, that the observations of Dutrochet clearly shew that the 

 nature of the septum exerts an important influence upon the direc- 

 tion of the predominant current. If the attraction of the septum 

 for the exterior fluid be the greater, the endosmotic current will 

 prevail, and vice versa. 



Endosmose is a more important agent in the vital phenomena 

 of plants than in those of animals. It is supposed, by some phy- 

 siologists, to be brought into play in the processes of secretion and 

 absorption. 



The animal membranes exercise the property of porosity in re- 

 ference to gases, as well as to liquids; and the tendency of dis- 

 similar gases to become diffused among each other manifests itself 

 even through compound textures. As in the case of liquids, there 

 is a double current, when two dissimilar gases are separated by a 

 porous septum, and the predominant current is that which has the 

 strongest attraction for the septum. The following experiments 

 illustrate this phenomenon: Confine some common air in a jar, by 

 tying tightly over it a piece of sheet-caoutchouc, and then place the 

 jar under a large bell-glass filled with hydrogen gas ; the hydro- 

 gen will gradually penetrate the partition, distend the caoutchouc, 

 and ultimately burst it. Or, suspend a membranous bag, the sto- 

 mach of a rabbit filled with common air, in an atmosphere of 

 carbonic acid ; the latter will penetrate to the former and burst 

 the bag. In both instances there is an exosmose greatly inferior 

 in the quantity of gas to the endosrnose. In respiration, this phe- 

 nomenon occurs at every inspiration through the walls of the pul- 

 monary air-cells and the plexus of capillary vessels distributed 

 upon them.* 



Although in the manifestation of these phenomena there is no 



* Dauiell's Chemistry. 



