220 A. V. LEBEDINSKY, V. M. MASTRYUKOVA AND A. D. STRZHIZHOVSKY 



seem to be represented by a coefficient less than 1 mnltiplied by the 

 probabihty K of division. However the temporal and dose dependence 

 of this factor have not yet been stndied. Most of the extracellnlar factors 

 exert their influence npon metabolism. Among them there exist the 



100 

 t 90 



c 

 o 



I 80 



o 



70 



Fig. 5. — Dej^endence of tlie number of lysed bone-marrow cells upon 

 time of rabbit aqueous humour on them : 



(a) before irradiation. 



(b) after irradiation. 



the 



exposure 



factors that contribute to the liquidation of radiation injury before the 

 start of the mitotic stage by affecting the intensity metabolism. There- 

 fore the apparent significance of radiation biological effectiveness will 

 decrease. Other things l)eing equal this effect is seen most clearly in the 

 cells with a longer duration of interkhiesis. It is highly probable that a 

 ]:)opulation of tliis kind may show with i)articular clarity the apparent 

 decrease of biological effectiveness under the corresj^onding extra- 

 cellular influences. From this point of view the mainly inhibiting action 

 of extracellular factors upon mitotic activity is worthy of attention. 

 Under their effect the intermitosis as it were lengthens, and thus the 

 temjioral iiossibilities for restoration from damage increase. 



The mathematical treatment of observations accumulated in study- 

 ing biological material and its phenomena necessitates certain approxi- 

 mations. We are forced to approximate consciously, not forgetting one 



