160 J. F. MCCLENDON. 



creased permeability and segmentation of the sea urchin's egg. 

 Therefore, from analogy, we may conclude that increase in 

 permeability may cause tissue cells to divide. 



The "wound stimulus" to regeneration of tissue may also 

 cause increased permeability of the cells. 



In a preceding chapter it was shown that the "current of 

 injury" produced by the negative electric potential of a wounded 

 surface is common to animal and plant tissues. The wounded 

 cell acts as an electric generator and a current flows through 

 neighboring cells. 



I observed that if a current is passed through living tissue, 

 which is subsequently fixed and stained, basophile substances 

 will be found displaced toward the anode. In sections of tissue 

 adjacent to a wound the extent of the current is indicated by the 

 displacement of basophile granules. The current affects first 

 the cells in contact with the wounded cells, then extends in some 

 directions more than others. Electric currents ("currents of 

 growth") continue for many days after the wound has healed. 



Since electric currents cause sea-urchin eggs and tissue cells 

 to divide and proliferate, probably these bio-electric currents 

 constitute the so-called "formative stimulus" of regeneration. 



Embryonic cells, cells of germinal regions, and cancer cells 

 are distinguished by their great power of proliferation, or rapid 

 division. It is probable that the plasma membranes of these 

 cells are more permeable than those of other tissue cells in the 

 same medium or under the same conditions. 



Cancers have been produced by the action of X-rays (electric 

 pulsations) on the skin. The cells in the skin were so changed 

 that they proliferated more rapidly. Similarly, electric changes 

 have been observed to start the egg cell to rapid proliferation. 

 There is probably some irreversible change in the permeability 

 of these cells, which does not, however, make the plasma mem- 

 brane incapable of subsequent reversible changes in perme- 

 ability (i. e., the change is unlike what occurs at death of the cell). 



The suggestion that cancer cells are more permeable than 

 tissue cells in general may possibly be of therapeutic importance. 

 Loeb has shown that fertilized eggs are more sensitive than un- 

 fertilized eggs to various toxic substances (probably 



