CHAP. I.] POROSITY. ENDOSMOSE. 53 



the water of the contained blood, which transudes into the sur- 

 rounding areolar tissue, and gives rise to that dropsical effusion, 

 which is commonly called Anasarca. In the minute capillary ves- 

 sels, this property is always present in a state of health, and the 

 nutrition of the surrounding tissues is effected by the exercise of 

 it. After death, the influence of porosity is favoured by the total 

 absence of motion in the fluids, and of vital change in the walls 

 of the vessels ; and, therefore, in the dead body, we find the 

 areolar tissue more or less loaded with water in all those places 

 in which gravitation favoured its accumulation. The progress of 

 decomposition, by disintegrating the tissues, also favours the occur- 

 rence of transudation. 



It is probable that certain vital processes consist solely in transu- 

 dation. In this way the watery part of the secretions doubtless 

 escapes from the blood-vessels, into the canals of the secreting 

 organs ; and this is especially likely as regards the mechanism of 

 the kidney, where the blood-vessels of the Malpighian bodies, 

 reduced to their minutest size, naked, and unassociated with any 

 other tissue, are most favourably placed for the occurrence of this 

 phenomenon ; and the absorption of fluids brought in contact with 

 certain surfaces is explicable on the same principle. 



The process, which was first described by Dutrochet, under the 

 name Endosmose and Exosmose, is intimately connected with the 

 porosity of animal tissues. It is a process, " in which the mutual 

 attraction of two liquids is called into action, one of which is more 

 capable than the other of freely wetting a porous solid which forms 

 part of the combination." * 



If an animal bladder, the caecum of a fowl, partially filled with 

 syrup, and tied tightly at its open end with a string, be suspended 

 in a vessel of water, it will soon be found distended almost to 

 bursting, in consequence of a considerable quantity of the water 

 having passed through the walls into the cavity of the bladder 

 (Endosmose). If the exterior fluid be examined, a portion of the 

 syrup will be found to have passed out of the bladder (Exosmose). 

 Or the phenomenon may be illustrated by the following experi- 

 ment : Take a funnel, and tie over its broad end (of three or four 

 inches' diameter) a piece of bladder, invert it, and fill it with spirits 

 of wine, and fit to its small end a glass tube, three or four feet in 

 length, and then place it in a vessel of water. In a short time the 

 water will be observed to rise in the tube, and it will ultimately 



* Daniell's Chemistry. 



