306 Mr. J. F. Gaskell. [ Nov. 11, 
Further evidence of a different kind supporting the view that the 
diminution occurs equally in all tissues will be given later in this paper. 
Table LI. 
BE TaNG Duration Number of Mitoses Mitotic index or 
BY of X-ray dose. cells counted. observed. number per 1000. 
1 Control | 2,738 79 288 
2 e 2,548 75 29 :°5 
3 Ae 2,576 ah 29 ‘9 
4, - 2,412 72 29 °8 
Total’. .c.ecveosncee 10,274 303 29 °5 
1 5 minutes 3,063 72 23 °5 
2 3 2,592 62 23 9 
3 + 2,625 62 23 °6 
Motal gag sces cbs eheneas 8,280 196 | 23-7 
1 1O minutes 3,769 66 TGs | 
2 is 3,953 75 18°8 
3 z. 1,877 39 20 °7 
Motalc wet cpesmaccnc ese 9,599 180 18 °7 
Other specimens were incubated for three days and then X-rayed for 
15 minutes, 30 minutes, and one hour respectively. The progressive 
diminution in mitotic activity was evident in these, though no actual 
counts were made. It appears, therefore, that a progressive diminution of 
mitotic activity takes place, under the influence of X-rays, in a rapidly 
growing organism such as the chick embryo. 
These results are contrary to those arrived at by Cattley* in the growing 
root tips of plants. He found that an increasing stimulatory effect was 
obtained + with increasing lengths of ‘exposure up to one of 30 minutes’ 
duration. From this point there was diminution, but not to a figure below 
that obtained in the controls until the exposure had lasted for two hours. 
His exposures were at a somewhat greater distance, 25 cm. from the anti- 
cathode, but this would not be a factor of sufficient importance to account 
in any way for the different type of results obtained. 
It is possible that an initial stimulant effect may occur in the chick embryo 
also; it must, however, be very brief; smaller doses than one of five 
* ‘Journ. of Path. and Bact.,’ April, 1909, vol. 13, p. 380. 
