ALIMENTARY TRACT AS AN ABSORPTIVE SYSTEM. 



and the concentration of this is allowed to increase slowly 

 through evaporation the algae suffer no change, for each in- 

 crease in the concentration of the glycerine solution has time 

 to be equalized by an increase in the concentration of the 

 glycerine within the cell. But if the algae be removed from 

 the now concentrated solution of glycerine and dropped into 

 clear water they burst at once, for in so short a time the 

 glycerine has not had time to diffuse out of the cells. 



Methyl alcohol belongs, on the other hand, to the sub- 

 stances which can rapidly pass through cell membranes. 

 The root hairs of Hydrocharis plasmolyze in a cane-sugar 

 solution having a concentration between 7 and 7J percent. 

 Plasmolysis occurs in the 7^ percent solution in 10 seconds. 

 If 3 percent of methyl alcohol are added to the 7 percent 

 cane-sugar solution its osmotic pressure is made to equal a 

 35 percent cane-sugar solution. Yet in this mixture of 

 sugar and methyl alcohol no plasmolysis occurs, for the 

 methyl alcohol diffuses almost instantaneously through these 

 cells so that the great difference between the osmotic pres- 

 sure within and without the cells cannot become effective. 



(OVERTON.) l 



To the compounds which diffuse rapidly into protoplasm 

 belong the monatomic alcohols, aldehydes, and ketones, the 

 hydrocarbons with one, two, and three chlorine atoms, the 

 nitroalkyls, the alkylcyanides, the neutral esters of inorganic 

 and many organic acids, anilin, etc. The diatomic alcohols 

 and the amides of monatomic acids pass into cells more 

 slowly, and still more slowly glycerine, urea, and erythrite. 

 /The hexatomic alcohols, the sugars with six carbon atoms 

 / (hexoses), the amino-acids, and the neutral salts of the organic 

 acids diffuse into cells only very slowly. The entrance of 

 these various substances into the cells is rendered apparent 

 by yet other signs than a failure of plasmolysis, such as evi- 

 dence of narcosis or other intoxication, the formation of pre- 



1 Cited from HOBER: 1. c., p. 105. 



