ANIMAL MEMBRANES. 7 



column at the same height, till at last the wide part 

 of the tube is emptied of water and filled with 

 mercury. 



Solution of salt, fat oil, alcohol, &c., behave ex- 

 actly as water does ; under a certain pressure these 

 fluids pass through an animal membrane, just as 

 water does through a paper filter. 



The pressure required to cause these liquids to 

 flow through the pores of animal textures depends 

 on the thickness of the membrane, as well as on 

 the chemical nature of the different liquids. 



Through ox-bladder, j^th of a line (rai^h of an The pres- 

 inch) thick, water flows under a pressure of 12 with dif- 

 inches of mercury ; a saturated solution of sea salt 

 requires from 18 to 20 inches; and oil (marrow 

 oil) only flows out under a pressure of 34 inches of 

 mercury. 



When the membrane used is the peritoneum 

 of the ox, -^th of a line (i^oth of an inch) in 

 thickness, water is forced through it by 8 to 10 

 inches, brine by 12 to 16 inches, oil by 22 to 24 

 inches, and alcohol by 36 to 40 inches of mer- 

 cury. 



The same membrane from the calf, jOT^n f a 

 ^ ne (i9 1 92 n( ^ f an inch) in thickness, allows water 

 to pass through under the pressure of a column of 

 water 4 inches high ; brine passes under a pressure 

 of 8 to 10 inches of brine, and oil under a pressure 

 of 3 inches of mercury. 



In making experiments of this nature, we observe 



