September 3, 1915] 



SCIENCE 



291 



ratory of Oskar Hertwig* at Berlin. Hert- 

 wig himself, his son G-iinther, and his 

 daughter Paula, and a number of his stu- 

 dents have performed an extensive series of 

 experiments over a wide range of forms and 

 have obtained results which are of the 

 greatest significance. In all of their work, 

 radium compounds have been the source of 

 the rays used for experimental purposes. 

 As a strong exposure to radioactivity is 

 always injurious to tissues, and since the 

 development of injured eggs gives rise to 

 malformation and produces monsters of 

 various degrees of deformity, much of the 

 experimental work is teratological in nature. 

 This is interesting from a pathological 

 standpoint, but is perhaps less fundamental 

 than the effects of the radiation on cells 

 (e. g., egg cells) and on their activity. On 

 both these phases of the study the work of 

 the Hertwigs has an important bearing. 



The theory which was developed by the 

 early work of the Hertwigs and which has 

 been the working hypothesis upon which 

 their subsequent studies have been made is 

 called by its author a "biological hypoth- 

 esis." The observation was made in the 

 first cytological studies that centrosomes, 

 spindles and other cell organs with the 

 single exception of the chromatin showed 

 little injury due to the action of the rays. 

 This conclusion was based on evidence from 

 the study of eggs and sperm of sea urchins 

 and of frogs; later the observations have 

 been extended to other forms. It led to the 

 assumption that the effect is a direct one 

 on the chromatin of the radiated cells, not 

 an indirect one as had been postulated by 

 Schwarz, and, further, that the seat of the 

 injury if not exclusively in the chromatin 

 is certainly chiefly there. Due to the fact 

 that a slight radiation of the sperm is suffi- 



8 A series of papers by 0., G., and P. Hertwig, 

 by Oppermann, Fraenkel, and Stachowitz in the 

 Arch. f. Mikr. Anat., Bd. 77 to Bd. 85, 1911-1914. 



eient to cause abnormalities in the emhryo, 

 it was held that the injured chromatin pos- 

 sesses the property of conveying the injury 

 to the egg cell when it fuses with it and 

 subsequently to the descendants of this cell, 

 for nuclear division provides the anechanism 

 for distributing the injury to all cells of the 

 body. In a sense, therefore, the original 

 injury tends to increase as development pro- 

 ceeds. Hertwig sees in the beta and gamma 

 rays of radium a reagent which affects the 

 nuclear substance of living cells even in 

 the slightest amount. Especially the chro- 

 matin is injured in its living properties by 

 the slightest exposure to radio-active rays, 

 and by a greater exposure is so changed 

 that it loses the capacity to grow and to 

 increase in the regular way by mitosis, and 

 undergoes a gradual degeneration into 

 which the cytoplasm is also drawn. 



It may be said that this hypothesis has 

 much morphological basis and that it is 

 sufficiently elastic to accord with many of 

 the observed facts; yet it is clear that no 

 real explanation of the phenomena has been 

 offered on this basis, for the problem is 

 simply pushed further back into the cell 

 and it is necessary to make clear how the 

 chromatin is injured and how the injury 

 accumulates with development. It is un- 

 doubtedly true also that other substances 

 in the cell than chromatin are injured, al- 

 though it may not be possible to attribute 

 the irregularities of later development to 

 them, as can be done in the case of the 

 chromatin. A comparison of this hypoth- 

 esis with the lecithin hypothesis, and criti- 

 cisms which have been made of each, may be 

 deferred until other facts have been brought 

 out. 



Eecently Oskar Hertwig" has brought to- 

 gether in a brief statement the facts most 



9 Hertwig, O., ' ' Versuehe an Tritoneiern ueber 

 die Einwirkung bestrahlter Samenfaden auf die 

 tierisehe Entwicklung, " Arch. f. Mikr. Anat., Bd.. 

 82, Abt. II., 1913. 



