142 PROTOPLASMIC ACTION AND NERVOUS ACTION 



within a minute or less the two can easily be distinguished 

 by their difference in size. The semi-permeability of 

 the plasma membrane is not impaired, although the 

 permeability to water is increased. The conditions of 

 this phenomenon are probably complex, and determined 

 by metabolic factors of unknown nature. The change 

 of permeability is progressive and occupies a considerable 

 time, some 20 minutes elapsing (at 20°) before it nears 

 its final stage; it is arrested by anaesthetics (chloral 

 hydrate, ure thane, alcohols) and by cyanide in higher 

 concentrations.' 



If the impermeability to water in this cell is due to 

 the presence of water-insoluble substances (lipoids or 

 cholesterol) in the surface-film, the change above would 

 indicate that these are altered or removed in part; i.e., a 

 change in the chemical composition of the surface layer 

 is to be assumed. The nature of this change is unknown ; 

 but Lyon's observation that the iodine-combining power 

 of the egg is decreased after fertilization'' may indicate 

 a decrease in certain unsaturated compounds which 

 would otherwise take up the iodine — possibly cholesterol 

 or unsaturated lipins (lecithin). The permeabiHty of 

 fertilized eggs to water can be artificially modified in 

 certain ways; it is decreased by anaesthetics (chloral, 

 ure thane, alcohols),^ a fact also indicating a dependence 

 on the lipoid-content of the protoplasmic surface-film. 



Chambers finds certain differences in the behavior of 

 fertilized and unfertilized echinoderm eggs in micro- 



^ R. S. Lillie, American Journal of Physiology, XL (1916), 249; 

 XLIII (1917), 43; XLV (1918), 406. 



2 Lyon and Shackell, Science, XXXII (1910), 249. 



3 R. S. Lillie, American Journal of Physiology, XLV (1918), 427. 



