134 HALSEY J. BAGG 
locephala. Gilman and Baetjer (8), after radiating the ova of 
Amblystoma, and Baldwin (9), the fertilized ova of frogs, were 
able to produce a fairly constant type of developmental defect. 
Injurious results have followed in all cases where mammals have 
been exposed to x-radiation. It has been shown that when any 
particular part of a young animal is exposed to a sufficient amount 
of radiation, that part fails to reach its normal size and is unable 
to exercise a full degree of function. 
Arrests in development and the production of abnormal types 
may be induced not only by radio-activity, but by many physical 
or chemical agents. Abnormal temperature changes, treatment 
by many chemicals, lack of oxygen supply, or the overabundance 
of carbon dioxide, ete., have produced marked changes in the 
developing embryo. 
The present experiments are mainly concerned with distur- 
bances in mammalian development, before and after birth, as a 
result of exposing the embryos of rats, at various times during 
the prenatal period, to irradiation from radium emanation. The 
effect on the embryos following radiation of the mother at varying 
intervals before mating was also determined. These experiments 
were designed not only to study the factors underlying the pro- 
duction of abnormal types, but through an examination of the 
abnormal to gain a clearer insight into the nature of normal 
development and differentiation.” 
I acknowledge with pleasure my indebtedness to Dr. James 
Ewing for his aid in the interpretation of the pathological results. 
METHODS AND APPARATUS 
Two methods were used for applying the radium emanation. 
In the first method an ‘active deposit’ was obtained by exposing 
a definite quantity of common salt to a comparatively large 
amount of radium emanation, about 500 millicuries were used, 
? Dr. J. F. Gudernatsch was a co-investigator with the writer during the year 
1919. A preliminary report of the work done with him at that time is given in 
the Proceedings of the Society for Experimental Biology and Medicine, 1920, 
vol. 17, p. 183. 
OO 
