A. RICHARDS. 



7. The depression never follows until a complete mitotic 

 cycle has been passed. Thus if the egg is exposed in the first 

 maturation mitosis the depression does not cccur until the first 

 cleavage. 



8. An egg may be stimulated during the depression phase by a 

 second exposure to the rays, but the new phase of acceleration 

 is less and the depression follows more rapidly. 



9. The control, started at the time of exposure, goes more slowly 

 than the experiment during the first two mitoses, but by the 

 time that the twenty-four cell stage is reached the exposed eggs 

 are progressing more slowly that it. 



10. It has not been found possible to account for these effects 

 on the basis of rise in temperature, and the nature of the experi- 

 ment practically eliminates other disturbing factors; therefore, 

 the effects must be regarded as the result of exposure to the X-rays. 



11. Analogy suggests that the effect of X-rays on cell divisions 

 may perhaps be due, partly at least, to the effect of the rays on 

 enzymes contained within the cell. 



DISCUSSION OF THE LITERATURE. 



Many observations have been made as to the effect of X-rays 

 and radium on growth and rather diverse results have been 

 obtained. Extensive bibliographies in which the previous work 

 has been quite thoroughly reviewed are to be found in the 

 following publications: Warthin, A. S. (International Clinics, 

 1906, I5th series, Vol. IV.); Gager, C. S. (Memoirs of New York 

 'Botanical Garden, IV., 1908); Bardeen, C. R. (Jour, of Exp. ZooL, 

 Vol. IV., 1908 and Amer. Jour. Anat., Vol. XL, 1911). As far 

 as I have been able to discover, few previous observations have 

 been made on the effect of radiation upon the rate of division. 

 Certain other observations have a less direct bearing but are in 

 line with the conclusions here reached. In view of these facts, 

 it seems necessary to discuss only a few of the papers on this 

 subject. 



Bacteria and yeasts have generally been found to be inhibited 

 by exposure to radiation if sufficient stimulus to effect them w T as 

 given. Koernicke, however, states that if the organisms be 

 transferred to fresh unexposed gelatin, they will grow again, and 

 Gager found budding in yeasts to be increased by exposure. 



