RADIUM IRRADIATION AND DEVELOPMENT Lar 
April 22, 1919, injected with 4.9 millicuries on May 7th, and was 
killed two days later. When the embryo was cut in serial section, 
it showed that the haematoma in the dorsal subcutaneous tissues 
had exerted sufficient pressure upon the spinal column to produce 
at one place a complete dislocation. Microscopical examination 
of the viscera showed no pathological changes. Not all the 
foetuses of a litter were affected in the same degree. In one case 
seven foetuses were found, three showing haemorrhagic lesions, 
two beginning to macerate, and two in the process of absorption. 
This variation in resistance was due either to the higher or lower 
vitality of the embryos themselves or to the amount of radio- 
activity which passed the placentae. In another case the foe- 
tuses, although injured, were carried to full term, and among a 
litter of six young, two were apparently normal and four showed 
haemorrhagic spots on the head, face, and along the dorsal mid- 
line of the body. 
3. Several young of a single litter showed areas of extravasa- 
tion and were born alive. Their mother died, however, and 
foster mothers refused to nurse them. 
4, Eight litters gave normal living young. This number is 
low, because, as previously stated, many pregnant rats were 
killed by the experimenter at various intervals after treatment. 
The average number of young per litter was 4.8, as compared 
with 6.5 per litter for the control rats, but the probable errors 
indicate that this difference is, very likely, not significant. Only 
one litter, containing four young, survived a treatment given 
seven days after mating. Several of the rats of this group, 
which had apparently escaped the full radium exposure during 
the uterine period or perhaps they were more resistant to it, when 
mated inter se produced litters of apparently normal young of 
normal fertility. The offspring of these animals, about twenty 
in number, were observed for two generations, but no abnormal- 
' ities were noted. 
II. Subcutaneous injections before mating. Seventy-seven fe- 
males were treated in this group, eleven died as a result of the 
injection before they were mated, while several were killed at 
weekly intervals after mating, and some were allowed to continue 
