THE BIOLOGY OF THE CELL SURFACE 



forms part of protoplasmic structure and how it plays a 

 role in protoplasmic activities. Since the structure of the 

 whole protoplasmic system Is composed so largely of 

 water, and its manifestations as a reacting system depend 

 so greatly upon water, this structure must in some way 

 dictate the distribution of water within the cell and hence 

 determine the entrance and exit of water. 



When by chance I saw drops of water leaving an egg-cell, 

 I was alert to seize the opportunity to follow by means of 

 simple observations the fate of water within the egg.^ 

 These observations will now be detailed and conclusions 

 derived from them. Also suggestions will be made con- 

 cerning the entrance of substances in solution into cells and 

 concerning the question, why cells take In certain substances 

 and not others. First, some mention should be made of 

 method. 



When unfertilized eggs of marine animals are placed in 

 dilute sea-water, they take up water and swell at a rate 

 which depends, for specific eggs, upon the degree of dilu- 

 tion. Thus, for the eggs of the sea-urchin, Arbacia, a 

 favorite object for this type of work, the rate of swelling in 

 40 per cent, sea-water (60 parts tap water plus 40 parts 

 sea-water) has been measured by LlUie- and confirmed by 

 others. After thirty minutes In this dilution the eggs 

 break down. If the sea-water is still more dilute, the water- 

 intake is more rapid and the eggs' break-down occurs earlier. 

 If the sea-water Is less dilute, the rate at which water enters 

 is slower and break-down comes on later. Thus I found 

 that in 60 per cent, sea-water Arbacia-eggs remain intact 

 for twenty-four hours. Unfertilized eggs of Echinarachnius 

 are more sensitive, being injured by dilutions which are 

 innocuous to Arbacia-eggs. 



^ Just, /g26b, ig2Sb, 1930a and h. 

 2 Lillie, R. S., 1916. 



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