OF VEGETABLE TISSUE. 27 



20. " Connected with the hygroscopicity of 

 vegetable membrane, we may here mention a 

 property* of all membrane, which has probably 

 a considerable influence in the economy both of 

 animal and vegetable life. When a membrane 

 is viewed under the highest powers of the micro- 

 scope, it appears to possess a perfectly homo- 

 geneous texture, without pores of any kind ; and 

 yet water, milk, and other fluids, placed under 

 certain circumstances, are capable of passing 

 through it with considerable facility. The con- 

 dition required for producing this effect are 

 these: Any two fluids which exert a mutual 

 affinity towards each other, being placed on oppo- 

 site sides of a membrane, their immediate inter- 

 mixture will commence, each of them passing 

 through the substance of the membrane. If, for 

 instance, a little treacle be enclosed in a piece of 

 bladder, and this immersed in water, a portion of 

 the treacle will soon be found to have exuded, 

 while a still larger quantity of water will have 

 penetrated into the bladder ; and this action will 

 continue until the fluids have acquired the same 

 density. The remarkable circumstance attend- 

 ing this phenomenon is the fact of the lighter 



* This property is called Endosmosis. 



