entr' acte 211 



glass is interposed or if the quartz lamella is covered with a 

 layer of gelatin. The effect can also be transmitted through 

 the reflections of a mirror. The increase in cell-division 

 appears exactly at that spot where it would strike if it were 

 a reflected ray. In such experiments pulp of onion roots 

 may be used in place of whole root to produce the same 

 effect. In the natural growth of the root, it is particularly 

 the tip which is growing. The experiments of Gurwitsch 

 indicate that this growing tip sends a radiation which acts' 

 on the second root. 



The description of this new biological phenomenon ex- 

 cited considerable interest and instigated numerous at- 

 tempts to repeat the experiments. However, considerable 

 difficulty was experienced, since the effect is by no means 

 readily observed. Numerous sources of error are present. 

 It is not astonishing, therefore, that some experimenters, 

 using the onion root method, have failed to find any mito- 

 genetic radiation at all. Most of those who have seen 

 positive results have obtained them only after initial nega- 

 tive observations. 



In the further development of this research, Gurwitsch 

 was assisted by many other scientists. They developed 

 other more reliable and more convincing methods and the 

 existence of such radiation was proved more definitely. 

 Most of these methods are based on the increased cell- 

 division of yeast. The conditions under which such radia- 

 tion is sent out were investigated with great care, in an 

 enormous number of observations by Gurwitsch and his 

 associates. They found that almost any living plant, ani- 

 mal, or part taken from them, may exhibit such radiation. 



However, the source of the radiation is not to be sought 

 in the active growth or in the cell-division of any living 

 thing. In fact tissues which are in active cell-division do 

 not give off rays. Hence the term mitogenetic rays, mean- 

 ing rays generated by cell-division, is really incorrect. On 

 the contrary, the rays are used to bring about cell-division. 



