294 



SCIENCE 



[N. S. Vol. XLII. No. 1079 



periments of the toad's and frog's eggs, 

 demonstrating that abnormal embryos re- 

 sult from radiation, and showing to a cer- 

 tain extent under what conditions they are 

 produced. The kinds of abnormalities are 

 described and experiments given to deter- 

 mine the periods of greatest susceptibility. 

 The following are among his most impor- 

 tant conclusions : 



These experiments shoiT conclusively that both 

 the male and the female sex-cells may be so al- 

 tered by the X-rays as to give rise to the forma- 

 tion of monstrous forms. The susceptibility of 

 the male and female sex-cells is approximately 

 equal, although the abnormalities appear earlier 

 in development and are greater when the ova are 

 exposed. After fertilization until cleavage begins, 

 the ova at first appear to be no more susceptible 

 than the sex-cells before fertilization. During the 

 earlier stages of cleavage the susceptibility of the 

 eggs to the X-rays is markedly increased, but dur- 

 ing the later stages of cleavage before closure of 

 the blastopore the susceptibility of the eggs be- 

 comes much less, and after the blastopore is closed 

 the power of the X-rays to influence development 

 becomes strikingly reduced. The period of great- 

 est susceptibility is the period during which there 

 is the most rapid production of nuclear material. 



Packard^^ has recently published an ac- 

 count of his experiments on the effect of 

 radium on the fertilization of Nereis. 

 These experiments were performed to as- 

 certain how "early the development of the 

 egg is affected by radium radiations when 

 (1) the sperm is exposed; (2) when the egg 

 is exposed; and (3) when the egg is ex- 

 posed immediately after fertilization." 

 His results are important, for he finds that, 

 in addition to the usual effects such as re- 

 tardation of development, multipolar spin- 

 dles and the like, not only chromatin, but 

 also the achromatic portions of the spindles 



ies on the Variation in Susceptibility of Amphibian 

 Ova to the X-rays at Different Stages of Develop- 

 ment," Amer. Jour. Anat., Vol. 11, 1911. 



12 Packard, Charles, "The Effect of Radium 

 Radiations on the Fertilization of Nereis," Jour. 

 Exp. Zool., 16, 1914. 



and the cytoplasm, show the effects of the 

 exposure. In eggs radiated before fertili- 

 zation, it may happen that the alveolar 

 layer of the cytoplasm is not extruded as is 

 normally the case in the eggs of Nereis. If 

 this occurs the maturation processes are 

 much modified, resulting in diverse forms 

 of chromosomes and spindles, with perhaps 

 small asters scattered about through the 

 cj^toplasm; and various other irregularities 

 may be present in the mitotic figures. Thus 

 it will be seen that Packard 's observations do 

 not all agree with those made in Hertwig's 

 laboratory. Parthenogenesis is not found 

 to occur in Nereis as the result of exposure 

 to radium, but it is a common observation 

 that the eggs of that animal are not as 

 favorable for parthenogenetic development 

 as are those of the sea urchin upon which 

 Hertwig worked. 



For various reasons the hypotheses of 

 both Hertwig and Schwarz are held to be 

 insufficient to account for the phenomena 

 observed by Packard, and he proposes an- 

 other explanation, suggesting "that the 

 radium radiations act indirectly on the 

 chromatin and protoplasm by activating 

 autolytic enzymes which bring about a de- 

 generation of the complex proteids, and 

 probably by affecting other protoplasmic 

 processes in the same manner." This hy- 

 pothesis is reached partly as a result of his 

 own experiments and partly from a con- 

 sideration of certain other work, and to 

 some extent takes a middle ground between 

 the other two, although in some phases it 

 differs sharply from both. Cells contain 

 a great many kinds of enzymes and it has 

 been shown by a number of investigators 

 that radium rays and X-rays have the 

 property of modifying the action oi some 

 enzymes. Packard concludes that while 

 many enzymes may be activated, "the lytic 

 enzymes are more stimulated than those 

 which play a synthesizing role." Where a 



