136 



ABSORPTION 



the walls of the blood and lyniph vessels themselves. The 

 manner in which this is accomplished involves a discus- 

 sion of certain peculiar physical processes known as osmosis 

 and dialysis. 



Osmosis and dialysis. — Tie a thin membrane, such as 

 parchment or the skin which a butcher uses to hold sau- 

 sage meat, tightly about the base of a student lamp chim- 

 ney. Then, into the top of the chimney fit a cork with an 

 eighth of an inch glass tube passing through a hole in its 

 center. Before fitting in the cork and tube, fill the base of 

 the chimney with water in which has been dissolved some 

 colored salt, such as potassium bichromate. Then insert 



the cork and tube. If the parch- 

 ment is tightly tied there will be 

 no leakage. Finally, suspend 

 this whole apparatus in a jar of 

 clear water so that the Uquid in 

 the jar and the chimney is at 

 the same level. If these direc- 

 tions are carefully followed, 

 the result will be an apparatus 

 such as is pictured in Fig. 47, 

 and the liquid in the chimney 

 will have a reddish-yellow color. 

 (See Ex. XXIX. ) If we let this 

 apparatus stand for a few hours, 

 at the end of that time we shall 

 be able to observe two curious 

 results. First, the level of the liquid in the chimney will 

 be higher than that in the jar; second, the clear water in 

 the jar wiU have become colored like that in the chimney. 

 Now it is evident that what has happened is not due to 



S^i^Jr 





FiC. 47— Dialyzer. 



