588 FRANK R. LILLIE 



allowed to point out the impossibility of regarding the interchange 

 between the egg and its enviroment as controlled exclusively by 

 diffusion through a semi-permeable membrane. However signi- 

 ficant the role of permeability of the membrane may be, my 

 experiments show that the egg cell is by no means bound in its 

 exchange to diffusible substances; but that the membrane must 

 be regarded as an active factor, and not only a passive one. 

 Twenty years ago diffusion was assumed to play the chief role 

 in the absorption from the intestine or in excretion by the kidney 

 epithelium. Today we know that the excretion of urea means 

 work by the kidney cell; it is an active, not a passive, process. 

 Similarly the secretion of fertilizin by the egg cell, and possibly 

 other cortical phenomena, must be regarded as active processes. 

 The ordinary chemical analysis of the cell begins with destruc- 

 tion of its more highly organized living constituents ; it is obvious 

 that such methods are inadequate for the investigation of the 

 immediate reactions in living protoplasm. The results of these 

 experiments may then gain a still broader interest if they may be 

 taken to indicate a method of studying such reactions by the use 

 of living cells as indicators. 



