2O2 RALPH S. LILLIE. 



bility must be assumed to exist in other tissues that show a 

 markedly periodic activity, t\ g., automatic -nerve centers like the 

 respiratory center, or contractile structures like cilia and con- 

 tractile vacuoles. The case of cell-division, as seen for example 

 in the cleavage of an egg-cell, is another instance of a rhythmical 

 process which, reasoning from the above considerations, one might 

 expect to find associated with, and perhaps conditioned by, a 

 periodically recurring increase of permeability. It is in fact note- 

 worthy that conditions which produce increased permeability in 

 other cells as shown by their stimulating or haemolytic action 

 very generally initiate cell-division in unfertilized eggs ; such are 

 the action of hypertonic solutions, of specific chemical substances 

 (weak acids, potassium salts, alkalis, various coagulative, cyto- 

 lytic and lipolytic substances), of mechanical treatment, of tem- 

 perature changes, and of the electric current under certain con- 

 ditions. 1 Loeb, in a remarkable series of experiments during the 

 past two years, has shown that, in addition to the class of lipoid 

 solvents, such substances as saponin, solanin, bile-salts, soaps, 

 foreign blood sera-- in general substances which, as shown by 

 their haemolytic action, increase the permeability of the surface 

 layers of cells may initiate cell-division in unfertilized ova. The 

 surface-layer of the egg first undergoes alteration with the sepa- 

 ration of a thin film --probably a haptogen membrane consisting 

 mainly of protein material the fertilization-membrane. Any 

 condition that produces this characteristic change may lead to 

 cell-division. The process by which the membrane is formed is 

 regarded by Loeb as of the same nature as the cytolytic process 

 which follows more prolonged action of the membrane-forming 

 solutions. 2 Cytolysis, however, may be simply a consequence of 

 loss of osmotic equilibrium, as above seen. The significance of 

 the fertilization-membrane has been the subject of much discus- 

 sion. The mere separation of a thin film from the egg-surface is 

 probably an accessory or accidental feature of the essential change 

 involved ; it seems clear, however, that one important effect must 

 result from the removal of such a layer of material from the 



1 Cf. the recent experiments of Delage, Archives de zoologie experimentale it gen- 

 erate, Ser. 4, T. 9, 1908, notes et revue, p. xxx. 



2 Cf. J. Loeb, Biochemis<he Zeitschrift, 15, 1909, p. 269. 



