9O A. RICHARDS. 



"2. Rontgen rays and radium rays produce similar physio- 

 logical results. 



"3. Sensitiveness to these rays varies with the species of either 

 plant or animal. 



"4. Younger, and especially embryonic tissues, are more 

 sensitive than those more mature. 



"5. With only one or two exceptions, exposure to radium rays 

 has been found to either retard or completely inhibit all cell- 

 activities. The rays may cause irregularities in mitosis. 



"6. Experimental evidence for or against the existence of a 

 radiotropic response is conflicting. 



"7. Whatever the immediate, internal change produced in 

 the protoplast may be, the result, with animals as well as with 

 plants appears to be more or less profoundly modified by the 

 presence of chlorophyll in the cell. 



"8. Radium rays appear to retard the activity of enzymes." 



Gager suggests in his final discussion of the results in his 

 memoir (p. 271) that "the rays may operate so as to increase or 

 decrease the amount of energy available for the work" (meaning 

 metabolic processes) "and, lastly, variations in growth may be, 

 either wholly or partly, expressions of the influence of the rays on 

 cell division." In the latter case growth would be an index as 

 to the effect of the rays on the reproductive functions of the cell, 

 and this, it would seem, is highly probable. 



He says also, "No one has yet succeeded in accelerating the 

 rate of cell division or in increasing its amount in a given tissue 

 by means of radium rays. The only results recorded are the 

 introduction of irregularities and complete inhibition." After 

 some discussion of this he says further, "Thus we should expect 

 a priori, a retardation and finally a complete inhibition of cell 

 division in all tissues exposed to rays of sufficient activity and for 

 a suitable period of time. And this is what has been observed 

 to occur. Theoretically we ought also to be able to accelerate 

 the process by suitable conditions of exposure, but such conditions 

 have not yet been discovered." Whatever the effect of radium, 

 that of X-rays is most positive in regard to its ability to accelerate 

 division, at least under certain conditions. 



His final paragraph is also of interest in this connection. He 

 says: 



