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The Action of X-Rays on the Developing Chick. 
By J. F. GASKELL, M.A., M.B. Cantab., M.R.C.P. 
(Communicated by W. H. Gaskell, M.D., F.R.S. Received November 11, 1910,— 
Read January 19, 1911.) 
(From the Pathological Laboratory, Leeds University.) 
This research was undertaken at the suggestion of Prof. Griinbaum, in 
order to discover whether any changes were produced in the chick embryo 
under the action of X-rays. Embryos of various ages were examined, both 
directly after exposure to doses of various amounts, and also at later periods. 
In none were any observations obtained of changes either in the embryo 
as a whole or in any particular organ, with the exception of one which 
affected all the tissues so exposed. 
It was found that X-rays had a general effect on the rate of division of the 
cells of the embryo, causing a diminution in the number of mitoses. This 
diminution was very evident in embryos exposed to long doses; for 
instance, chicks incubated for three days and then given a two hours’ 
exposure, showed so marked a diminution that a considerable search was 
required to find any mitotic figures, while in an embryo of three days, 
exposed for four hours, no mitotic figures could be found. 
In order to discover whether this diminution was progressive from the 
beginning of the exposure, or whether initially an increase of mitotic activity 
occurred, small doses of 5 and 10 minutes were given to embryos of four 
days. These were used with their controls for the purpose of making 
quantitative counts. The fore-brain was selected as the most suitable tissue 
for counting owing to the regular arrangement of the cells. That portion 
only was counted which was of fairly uniform thickness, and, as far as 
possible, median sagittal sections only were used for counting, in order to 
count only cells cut in their principal plane. The sections were cut 5u 
thick and cells were counted by their nuclei. The results of the counts 
are shown in Table I. The eggs were exposed at about 20 cm. distance from 
the anti-cathode. 
The figures obtained do not show very wide variations in each individual 
count, so that they should be sufficiently reliable to establish the fact that 
there is a progressive diminution of mitotic activity even with small doses. 
Counts were also attempted on the alimentary canal and the liver, but 
the difficulties of counting and the number of cells available did not give 
reliable figures ; the same tendency to diminution was, however, observed. 
