296 



SCIENCE 



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



Similar explanations have been suggested 

 by others, e. g., by Hippel and Pagen- 

 strecher^^ who find that ic-radiation of rab- 

 bits produces an eiSect similar to that result- 

 ing from cholin injection and think that a 

 toxin is developed which is transferred 

 from mother to embryo, to the injury of 

 the latter. The facts already brought out 

 here show that this explanation is not a suffi- 

 cient one, nor one of general application. 



The objections to Hertwig's biological 

 hypothesis are less serious than in the case 

 just discussed, and they would scarcely hold 

 against it in a less extreme form. It is, of 

 course, true that the solution offered by 

 Hertwig is incomplete in that it does not go 

 far enough back into the organization of the 

 cell; for, even on the assumption that the 

 chromatin is the chief seat of injury, fur- 

 ther explanation, which must ultimately be 

 chemical in nature, is required to show how 

 the injury is communicated to other parts 

 of the cell and what the mechanism is by 

 which its action is manifested. 



According to the Hertwig hypothesis, 

 chromatin above everything else in the cell 

 suffers injury from radiation and the patho- 

 logical conditions in the embryo are trace- 

 able to the injured chromatin, which may 

 be regarded as a " contagium vivo ' ' increas- 

 ing, ferment-like, at each division.^* Thus 

 the mechanism of the cell provides the 

 means for distributing the injury to each 

 successive cell generation and for carrying 

 it to all parts of the embryo. 



To this theory, Packard has offered two 

 criticisms. The concept, that the injured 

 chromatin or a substance produced from it 

 acts as a contagium vivo, is scarcely a solu- 

 tion of the problem, for it merely restates 

 in another form certain facts observed and 

 presents a picture of the problem itself 

 from a different viewpoint without giving 



13 Munchner Med. Wochenschr., No. 10, 1907. 



14 Hertwig, 0., ' ' Die Eadiumkrankheit tierisoher 

 Keimzellen, " Arch. f. Mikr. Anat., Bd. 77. 



any explanation of the facts. It should 

 again be pointed out that the ultimate solu- 

 tion must be chemical in nature. Packard 

 also questions the assumption that the in- 

 jurious substances developed in the nucleus 

 must remain there and can not involve 

 purely cytoplasmic structures even during 

 division (for a normal haploid division of 

 the egg chromosomes takes place if the 

 radiated sperm head does not mechanically 

 interfere in the spindle). A condition con- 

 trary to this assumption is given by Pack- 

 ard, showing that cytoplasmic structures are 

 changed in Nereis eggs, for example in the 

 case of eggs radiated before fertilization' 

 which fail to give off the alveolar layer and 

 thus extrude the jelly as they should do. 

 Obviously here the injury has been commu- 

 nicated to the egg cytoplasm, and is not in 

 accord with the Hertwig assumption. 



But the most serious objection to the 

 Hertwig theory as it now stands lies in the 

 fact that other than nuclear structures and 

 substances are affected by X-rays and the 

 radium rays. The failure to extrude the 

 alveolar layer in Nereis eggs is a ease in 

 point, and in the same eggs abnormal spin- 

 dles and asters occur as a consequence of 

 radiation. It has been found by numerous 

 investigators that radium rays have the 

 power to affect enzymes, and the writerf^^ 

 has shown that X-rays are able to bring 

 about modification in the activity of certain 

 enzymes. Enzymes are derived from living 

 tissues, and if it is possible to cause their 

 modification outside of the cell by the use 

 of radioactivity it is not improbable that 

 they also undergo change while within the 

 cells. In fact, the writer working with Miss 

 "Woodward^^ was able to prove that X-rays 



15 Eiehards, A., ' ' The Effect of X-rays on the 

 Action of Certain Enzymes, ' ' Amer. Jour. Fhysiol., 

 Vol. 35, 1914. 



16 Richards, A., and Woodward, A. E., "Note on 

 the Effect of X-radiation on Fertilizin, " Biol. 

 Bull., v., 28, 1915. 



