392 BIOLOGICAL EFFEVTS OF RADIATION 



In an extensive series of experiments by O. Hertwig and his associates 

 and by Packard the effect of radiating germ cells previous to fertilization 

 has been carefully investigated. In the frog 0. Hertwig (52) and 

 G. Hertwig (48) found that radiation of either spermatozoa or ova previ- 

 ous to fertilization resulted in fewer abnormalities than when the fertilized 

 egg was radiated. In addition, they made the surprising discovery that 

 when normal ova were fertilized with spermatozoa, which had been 

 radiated for a long time, the resulting abnormalities were fewer than when 

 the spermatozoa had been radiated for a short time. In other words, 

 the longer the radiation, the fewer were the abnormalities which resulted; 

 the shorter the radiation, the greater were the number of abnormalities. 

 This paradox was explained by the Hertwigs as follows: In the case of 

 short exposures the chromatin content of a spermatozoon was so injured 

 that after fertilization it was unable to function normally, it interfered 

 with the normal movement of the egg chromosomes, and abnormal 

 development of the fertilized egg ensued. On the other hand, if the 

 radiation of a spermatozoon had been for a long period of time, for exam- 

 ple, as long as 12 hr., then the chromatin of the spermatozoon was so 

 thoroughly injured that it took no part at all in fertilization. In this 

 case a spermatozoon simply served as an activating agent which incited 

 the egg to development without the fusion of male and female chromatin. 

 Development, therefore, was purely parthenogenetic. Likewise, the 

 Hertwigs found that in the case of radiated ova which were fertilized with 

 normal spermatozoa the damage which was produced was inversely 

 proportional to the length of exposure. The longer the ova were exposed, 

 the fewer were the abnormalities. Ova exposed for 15 min., for example, 

 gave more abnormalities and lived a shorter time than ova radiated for 

 several hours. The Hertwigs concluded that in this ease, as in the case 

 of the spermatozoa, the longer exposures so completely injured the 

 chromatin of the egg nucleus that after fertilization the female chromatin 

 failed to fuse with the male chromatin and, therefore, took no part in 

 development. The development of the egg in such a case as this, there- 

 fore, was androgenetic. 



The early conclusions of the Hertwigs, which were based on their 

 experiments on amphibian spermatozoa and ova, were without cytological 

 evidence, but later G. Hertwig (49) repeated the experiments, fertilizing 

 normal sea-urchin eggs with radiated spermatozoa. He was able to 

 demonstrate clearly that sea-urchin ova which were fertilized with 

 radiated spermatozoa developed parthenogenetically. Development was 

 often abnormal, however, because of a rather passive interference by the 

 abnormal sperm head. Other experiments, in which either the sperma- 

 tozoon or the ovum was radiated before fertilization, were made by 

 P. Hertwig (56) using the eggs of Triton and the frog and by Oppermann 

 (70) using trout eggs. Recently Simon (87) and Dalcq (35) have repeated 



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