44 



PHYSIOLOGY. 



to the current from without to tvithin^ while exosmos3, or transuda- 

 tion^ signifies the passage of the fluid from ivithin to without. 



In order that these phenomena may present themselves, the fluids 

 must be of different densities^ and miscible with each other ; and 

 under these circumstances the current is most rapid, as a general 

 rule, from the rarer to the denser fluid, and it continues until the 

 fluids are of equal density on both sides. 



There must also be an affinity between the membrane and the 

 fluid, otherwise no current will take place. 



It is not membranes only which are endowed with this property ; 

 very thin plates of slate, or of baked clay, produce the same effect, 

 though in a more feeble degree. Calcareous and siliceous laminse 

 have no effect of this kind. In membranes, endosmose is produced 

 till they begin to putrefy, when the phenomenon entirely ceases, and 

 the liquid which had risen in the tube descends, and filters through 

 the membrane. 



Of all the organic substances soluble in water, albumen produces 

 endosmose with the greatest force. It has also been proved by 

 Dutrochet, that, all other things being equal, the force which pro- 

 duces endosmose is proportional to the excess of the density of the 

 interior liquid over that of the water. Various theories have been 

 produced to account for these phenomena. Dutrochet's hypothesis, 

 that electric action is concerned with these phenomena, has not been 

 confirmed. The theory of Poisson, that endosmose depended on 

 capillary attraction, is, according to Matteuchi, inadmissible. " Pois- 

 son supposed that the least dense liquid entered the capillary tubes 

 of the membrane, and that this capillary thread, drawn down by 

 the pure water, and up by the denser liquid, must be elevated in 

 virtue of molecular attraction. But this explanation is inadmissi- 

 ble, when we consider that alcohol, which is lighter than water, pro- 

 duces endosmose ; and that certain calcareous and siliceous stones, 

 placed under the same conditions as membranes and plates of clay, 

 do not give rise to the same effects."* According to the same 

 author, up to the present time there is no satisfactory theory of 

 endosmose, though many physiologists accept that of capillary 

 attraction. 



" Experiment proves that the current of endosmose is not pro- 

 duced by the least dense liquid, nor by the most viscid one, nor by 

 that which is endowed with the greatest force of ascent in capil- 

 lary tubes. The current is in general determined by the liquid 

 which has the greatest affinity for the interposed substance, and by 

 which it is imbibed with the greatest rapidity. In fact, it is evident 

 that the membrane imbibes the two liquids unequally ; and that the 

 one which is imbibed with the greatest facility, ought to mix with, 

 and augment the volume of the other."t 



* Matteuchi's Lectures, p. 39. t Op, cit., p. 39. 



