ENTR ACTE 209 



life. The discovery of artificial parthenogenesis is one of 

 these disappointing developments; all it has taught us is 

 that a certain corrosion or destruction of the surface layer 

 of the ovum may initiate its development, even in the ab- 

 sence of fertilization. This feature is also brought out by 

 experiments on the artificial parthenogenesis of frog's eggs. 

 The procedure carried out in this case consists in puncturing 

 the eggs with a glass thread. It is a very crude method 

 which works only in a very few cases. We can learn from 

 these experiments that a mechanical impulse suffices to set 

 the development of the ovum going, at least in some in- 

 stances. Although not much has been learned about the 

 mechanism of fertilization, we may look forward to future 

 developments in the light of which we may hope to obtain 

 a better understanding of the true significance of these 

 vital processes. 



THE MITOGENETIC RAYS 



For many years Alexander Gurwitsch, formerly professor 

 of histology at Moscow, now at the Institute for Experi- 

 mental Medicine at Leningrad, had studied the incidence of 

 cell-division in tissues under various conditions. His sys- 

 tematic investigations led him to the assumption that the 

 immediate impulse which causes a cell to divide is not 

 generated within the cell, but comes from an outside source. 

 In order to divide, the cell must have manifestly reached a 

 certain developmental stage, but even if it is ready and pre- 

 pared to divide, Gurwitsch believed it took an impulse from 

 the outside to set the division going. It seemed difficult, 

 however, to find definite support for this assumption. 



Finally in 1923 Gurwitsch resorted to a daring experi- 

 ment in order to substantiate his view. He tested the pos- 

 sibility whether that extraneous impulse was transmitted 

 to the cell in the form of a radiation. The outcome of this 

 test, when performed under carefully controlled and favor- 

 able conditions, was successful in demonstrating the pos- 



