190 LABORATORY GUIDE IN PHYSIOLOGY. 



evaporating dishes; distilled water; sodium chloride; 



alcohol; egg; mercury manometer. 

 2. Preparation. 



(1.) Fit four of the dialyzers with membrane of pig- 

 bladder. The bladders should be carefully selected as 

 to uniformity in thickness, and should be soaked for 

 an hour or more in water before being stretched upon 

 the dialyzers. The membrane should be stretched as 

 nearly uniform as possible upon the four dialyzers. 

 Fit one dialyzer with parchment paper such as is fre- 

 quently used for this purpose. Furnish one dialyzer 

 with some other animal membrane e. g., a cow's blad- 

 der or a rabbit's caecum. 



(2) Prepare dilute egg-albumin by adding to strained 

 undiluted albumin about 9 volumes of distilled water. 



j. Experiments and Observations. 



(1) Salt, in saturated aqueous solution may be put 

 into a dialyzer. So adjust the apparatus that the 

 water in the outer receptacle shall be on a level 

 with the solution in the vertical tube of the dialyzer. 

 How much does the water rise in the tube ? What 

 degree of positive pressure within the dialyzer does 

 that represent? How much pressure per unit area, 

 measured with a mercury manometer will it be nec- 

 essary to produce within the dialyzer to stop the in- 

 crease of the volume of its contents? {Endosmotic 

 pressure.'} Will that amount of pressure prohibit 

 diffusion between the liquids? 



(2) After osmosis has been allowed to take its unim- 

 peded course for, say, one hour, starting with a 20 per 

 cent, solution of NaCl within and distilled water with- 

 out the dialyzer, note the height of the water in the 

 tube and compute the number of grammes of water 

 which have entered the dialyzer. Determine how 



