286 ABSORPTION. [CHAP. xxvi. 



was placed on the opposite side ; the proportions being about as 

 six to five. On the contrary, when solution of white of egg 

 was used, water passed more readily, when placed in contact with 

 the attached or submucous surface than when in contact with the 

 free or epithelial surface. It passed also towards the albumen in 

 only half the quantity that it did to the sugar. Again, with a 

 solution of gum, the endosmose was very feeble whichever way the 

 membrane was turned and seemed to follow no rule. 



These facts shew the influence exerted by the structure or 

 chemical properties of the membrane in this process ; but we are 

 still very much in the dark as to the intimate cause of the influence 

 thus operating. 



They are sufficient, however, to indicate the extremely im- 

 portant principle in physiology, that the chemical and structural 

 properties of the tissues exert a great influence on all those pro- 

 cesses in which the molecular motion of fluids is concerned. 



The thickness or thinness of the membrane also much affects 

 the result, and that for an obvious mechanical reason. If the 

 transmission of fluids is so rapidly carried on out of the body, 

 through the entire thickness of compound and dense membranes, 

 how much more expeditious must it be in the living tissues, where 

 the external fluid has in general but one or two very attenuated 

 films of membrane to traverse in order to arrive within the capillary 

 blood-vessels. 



Absorption as influenced by Pressure. The influence of pressure 

 on the passage of fluids through membranes, is illustrated by a 

 common filter, or by tying a membrane over one end of a vessel 

 containing fluid, to which a syringe capable of applying various 

 degrees of pressure is adapted. In the latter case, the rapidity of 

 transmission will be found, cceteris paribus, to depend on the 

 degree of pressure employed, and after a certain time the trans- 

 mission will be accelerated by the enlargement of the pores of the 

 membrane. In this way, pressure may be used as a test of the 

 relative transmissibility of different fluids through membranes of 

 various thickness and quality, and Liebig has found that " through 

 ox-bladder, p^th of an inch thick, water flows under a pressure of 

 twelve inches of mercury ; that a saturated solution of sea salt 

 requires from eighteen to twenty inches; and that marrow oil 

 only flows out under a pressure of thirty-four inches of mercury. 



" When the membrane used is the peritoneum of the ox, gi^th 

 of an inch in thickness, water is forced through it by eight to ten 

 inches, brine by twelve to sixteen inches, oil by twenty- two to 



