Septembeb 3, 1915] 



SCIENCE 



295 



slight radiation results in acceleration, the 

 synthetic processes may be supposed to be 

 stimulated more than the destructive activ- 

 ities. This hypothesis is essentially chem- 

 ical in nature and seeks to explain the 

 morphological effects observed in the cells 

 as the indirect result of enzymotic activity 

 under the influence of the radiation. 



Various new arguments for and against 

 these lij'potheses and theories have been 

 brought out as new facts have developed. 

 It is, therefore, necessary to consider the 

 more important points critically. 



The lecithin hypothesis was established 

 on the basis of an experiment by Sehwarz, 

 showing that in the chicken egg yolk, con- 

 taining lecithin, is broken down under the 

 influence of radium. Against this hypoth- 

 esis numerous objections are now to be 

 raised. Hertwig pointed out that the de- 

 composition was not determined by strict 

 chemical methods, and Neuberg also criti- 

 cizes it on chemical grounds, for lecithin is 

 itself so unstable that only a very accurate 

 chemical study could determine whether its 

 decomposition was actually due to the 

 radium radiation. 



If the seat of the injury were in the yolk, 

 little effect could follow radiation of the 

 sperm before fertilization, for the sperm at 

 most contains but little lecithin, and eon- 

 trarily, much greater injury should result 

 when the egg is radiated. As a matter of 

 fact, there is very little difference between 

 the results on the embryo, whether it is the 

 egg or the sperm that is radiated before the 

 fertilization. Egg nuclei are equally capa- 

 ble, with those of the sperm, of contributing 

 the chromatin by which the parthenogenetic 

 development previously described takes 

 place, both at first are able to start the de- 

 velopment of the egg so far as the heredi- 

 tary units are concerned, and injuries aris- 

 ing from the disturbance of either are 

 equally great. 



Very little lecithin could be decomposed 

 when so short a radiation of the sperm as 

 a minute was employed, as by G. Hertwig ; 

 yet this radiation was sufficient to cause 

 marked departures from the normal in the 

 embryo. That no chemical poison is gener- 

 ated by lecithin decomposition is obvious, 

 for in the ease of the short radiation of the 

 sperm the poison would be too dilute to 

 cause effects equal to those resulting from 

 longer radiation of the egg. 



The lecithin theory takes no considera- 

 tion of the fact that the most careful cyto- 

 logical study shows no morphological evi- 

 dence of yolk destruction; nor of the fact 

 that nuclei and especially chromatin do 

 suffer marked changes as the results of the 

 radiation. On the latter point all investi- 

 gators agree, and it must be explained by 

 any hypothesis which seeks to account for 

 the changes produced. Furthermore, yet 

 other cell constituents are acted on by radia- 

 tion, for cell extracts and cell enzymes have 

 been shown to be activated or retarded in 

 their action, depending upon the conditions 

 of the experiment. 



In this connection, it is by no means clear 

 how lecithin decomposition within the egg 

 could prevent, as Packard found radiation 

 to do, the extrusion of the alveolar layer of 

 the cytoplasm, a phenomenon depending 

 upon activities at the surface of the egg. 

 And finally, it is not possible to account on 

 this basis for the elimination of the sperm 

 head from development, or for the fact that 

 somatic nuclei of radiated Triton embryos 

 contain only half or the reduced number of 

 chromosomes. 



Most of these arguments against the leci- 

 thin hypothesis were, of course, unknown 

 at the time it was proposed. They are so 

 much at variance with it, however, that it 

 seems impossible to give it further serious 

 consideration. It may be regarded as com- 

 pletely overthrown. 



