152 HALSEY J. BAGG 
to an average size. The lungs, liver, kidneys, ete., had dif- 
ferentiated before the physical agent was employed. Further 
studies with earlier prenatal treatments should throw some light 
on establishing the critical growth periods of the various embry- 
onic structures. 
As a final point, the results of this investigation may be of 
interest to the clinicians and the laboratory workers who handle 
large quantities of radium and utilize x-rays. Although the 
results of this paper deal only with irradiation of the female, there 
is no reason to believe that the germ cells of the male are more 
resistant to these destructive agents than those of the female, 
and, in fact, there is very good experimental evidence to show that 
spermatozoa of some animals are especially likely to produce 
abnormal young after exposure to comparatively small quantities 
of irradiation. Physicians should guard against the possibility 
of producing developmental arrests such as shown in this article 
when treating pregnant women, as well as. the possibility 
of altering the human germ cells by irradiation previous to 
conception.? 
CONCLUSIONS 
1. The marked selective action of radium emanation on fast- 
growing embryonic structures was noted in these experiments. 
2. Very decided developmental arrests occurred in the dif- 
ferentiation of the nervous and reproductive systems of mamma- 
lian embryos exposed to irradiation towards the end of pregnancy. 
3. Experimental animals with greatly reduced, or practically 
no neopallium, gave apparently normal neurological behavior, 
except for blindness. 
4, Radium emanation, used either in the form of a radio-active 
solution injected into the adult female, or employed as an external 
3 The writer does not mean to be understood as stating that present-day clinical 
irradiation treatments produce such effects in the developing young, but it is 
his personal opinion that such changes are biologically possible. It is not pos- 
sible to obtain desired information by comparing the amount of exposure that 
a small mammal can stand with the corresponding dose that a man should tolerate, 
judging by comparative weights. The small mammal can tolerate very much 
more radiation in proportion to its weight than a man can. 
