390 BIOLOGICAL EFFECTS OF RADIATION 



mined, and little attention was given to the influence of external 

 factors other than radiation, such as change of temperature or chemical 

 changes in the medium. Only rather recently have investigators been 

 occupied with the collection of reliable quantitative data with regard to 

 the effect of specific dosages on specific phases of embryonic development. 

 It is this field which at the present time offers the greatest possibilities 

 for future research. 



So far as known to the writer, the first recorded observations of the 

 action of radium or of X-rays on embryonic development are those of 

 Bohn (22, 23), who submitted amphibian larvae and also the ova of the 

 sea-urchin, Sirongylocenirotus lividus, to the action of radium bromide. 

 Bohn simply floated a glass tube containing a few centigrams of radium 

 bromide on the water of a dish in which he had placed the larvae or the 

 eggs which he used. He found that the general effect was a retardation 

 of growth. Moreover, as a result of the radiation many of the amphibian 

 larvae died in later stages of development and others developed into 

 monsters which exhibited various abnormalities. With regard to the 

 developing eggs of the sea-urchin he made the following generalizations. 

 If the developing eggs were radiated before they began to gastrulate, 

 development progressed only as far as gastrulation and then ceased. 

 If gastrulation had already begun at the time of radiation, it might be 

 completed, but the larvae which developed were abnormal. Bohn also 

 exposed the ova and the spermatozoa of the sea-urchin before fertilization, 

 and reported that the ova withstood the radiation better than the 

 spermatozoa. In a few cases he found artificial parthenogenesis induced 

 by the radiation. 



After the work of Bohn, several other investigators soon entered the 

 field. Perthes (79) studied the ova of Ascaris, Schaper (85) studied the 

 eggs and larvae of the frog and the newt. Oilman and Baetjer (39) worked 

 on the developmental stages of the newt and the chick, and Tur (89) and 

 Bordier and Oalimard (25) also studied the developing chick. 



The work of Schaper (85), which was completed after Schaper's death 

 by Levy (63), represents one of the more critical of the early studies, and 

 has served as a basis for subsequent work on amphibians. Schaper used 

 larvae of the frog and the newt which he subjected to the action of radium 

 bromide. He found that development was retarded, and that in later 

 stages many developmental abnormalities appeared. These abnormali- 

 ties were associated especially with the neural tube, the retina, the olfac- 

 tory organs, the heart, and the blood vessels. Schaper and Levy extended 

 their investigations to include a study of the action of radium in pre- 

 venting regeneration in amphibian larvae, and also made some of the 

 earliest observations on the effect of radium in suppressing mitosis. 



Oilman and Baetjer (39) in their study of the effects of X-rays on the 

 development of the newt and the chick reported that in each case there 



