86 CHARLES PACKARD 



are found chiefly in the rapidly growing structures, such as em- 

 bryonic or regenerating tissue. The nature of the injury has 

 been studied particularly in the former type, and the generaliza- 

 tions made on the effect of radium radiations have been based 

 chiefly on such investigations. A study of the cytological details 

 of the changes thus brought about has been the point at issue in 

 the most recent studies on this subject and is the object of the 

 present investigation. 



THE NATURE OF THE RADIUM RADIATIONS 



A discussion of the nature of the radium radiations need not 

 be entered into fully in this paper. It may be mentioned simply 

 that the three types of rays apparently produce rather different 

 effects. The alpha rays, which form the greatest part of the 

 energy given off, are wholly shut out bj^ the glass or mica screens 

 which are usually arranged for the protection of the salt. As 

 the apparatus used in the following experiments and in the in- 

 vestigations of all those who used living tissues as an object for 

 study effectually screened the alpha rays, they may be disre- 

 garded in this discussion. The beta and gamma rays are able to 

 penetrate thin glass, but their activity is greatly diminished in 

 the transit. Their effect on protoplasmic activities is, in general, 

 an injurious one, although Congdon ('12) found some evidence of 

 acceleration in the rate of development in the eggs of Drosophila 

 due to the secondary gamma rays. In this case only the eggs 

 which received a very weak stimulus were accelerated. The 

 injurious effects found by practically all observers will be dis- 

 cussed in the next section. 



HISTORICAL REVIEW 



It has been found that different tissues show a great diversity 

 in the nature of their response to the radiations of radium. Thus, 

 the spermatogonia and the spermatocytes in the testis of the rat 

 may be killed or greatly injured while the surrounding Sertoli 

 cells and the connective tissue show no effects whatever. The 

 same is true for ova and the follicle cells. Kornicke ('05) who 

 exposed to radium the growing root tips of Lilium for periods of 



