Ij6 CHARLES PACKARD. 



But it has been demonstrated that very definite proportions of 

 these rays are actually absorbed by cells of deep-lying tissues. 

 And histological study shows that such cells after radiation im- 

 bibe water, swell considerably, and undergo degenerative changes 

 which have all the appearance of a typical cytolysis. It is appar- 

 ent, then, that any kind of rays which are absorbed produce the 

 same effects. But these more penetrating rays differ from the 

 less penetrating types in this respect, that they are also able to 

 bring about degenerative changes in the interior of the cell, par- 

 ticularly in the nucleus, which the latter, because of their slight 

 penetrating power, are unable to produce. 



I have mentioned the fact that a brief radiation with the slow 

 beta rays produces an acceleration in the division rate of Paramas- 

 cium. This effect is not restricted to the action of these par- 

 ticular rays, for all the radiations of radium, as well as X-rays, 

 can produce this result if the proper exposure is made. This has 

 been demonstrated in a great variety of cases, some of which have 

 already been cited. According to Lillie (16) such acceleration is 

 the direct outcome of increased permeability, for this condition 

 allows a freer interchange of CO2 and through the surface layer 

 and a consequent hastening of all metabolic activities. It may 

 be possible, therefore, that all cases of stimulation following 

 exposure to radium radiations and to X-rays can be explained on 

 this basis. 



SUMMARY. 



1. The susceptibility of Parafticecium to radium radiations 

 (chiefly the slowest beta rays) varies with the temperature at the 

 same rate as do physiological reactions of various kinds. 



2. The susceptibility also varies directly with the degree of 

 permeability of the surface layer of the cell. 



3. The slow beta rays act on the surface layer of the cell, in- 

 creasing its permeability, and if allowed to act long enough, 

 causing a typical cytolysis. In this respect they resemble other 

 types of radiant energy, and diverse chemical cytolytic agents. 



4. Cells which have a relatively high permeability are more 

 susceptible than those having low permeability, for the cytolytic 

 action of the rays is quickly followed in the former by a cytolysis 

 which is irreversible, while in the latter it is reversible. 



