RADIUM IRRADIATION AND DEVELOPMENT 135 
or the amount of radium emanation initially equivalent to one- 
half a gram of radium metal. To the radio-active salt thus pro- 
duced sufficient water was added to make a physiological solu- 
tion. The pregnant rats were injected subcutaneously in the 
shoulder region and intravenously through the caudal vein; 3 to 4 
minims constituted the usual dose. Because of the rapid loss of 
radio-activity of these solutions, the injections were made im- 
mediately after the preparation. The details involved in pre- 
paring and measuring the doses, as well as the methods for pro- 
tecting the experimenter, are described elsewhere (16 and 11). 
The activated solution exhibited all the known phenomena of 
radium metal itself; alpha, beta, and gamma rays were present, 
but the greatest physiological effects were probably due to alpha- 
ray activity. After long experimentation, a dose of 5 millicuries 
was found to be the maximum applicable to the aims of this experi- 
ment. In the second method gamma-ray radiation was applied 
through the ventral body wall of pregnant rats at nearly full term. 
A large amount of radium emanation was used, an amount equiv- 
alent to 14 grams of radium metal, filtered by 2 mm. of lead and 
3 mm. of silver. The source of emanation was 1 cm. away from 
the animal. The applicator, called a ‘lead tray’ in clinical usage, 
was 6 cm. in diameter and 1.5 em. high. This was placed in the 
bottom of a small wire cage, 10 by 13 em. in diameter and 10 cm. 
high, and was covered by a thin sheet of cardboard. The animal 
was placed on this paper immediately above the applicator. 
Preliminary tests showed that a dose of about 1300 millicurie 
hours was sufficient to produce developmental arrests in the 
embryos without killing the pregnant animals. Doses as high as 
2900 me. hrs., however, were successfully used in some cases. 
The embryos were killed by ether, and histological material pro- 
cured at various periods after the treatment. The tissues 
were fixed in Bouin’s solution, cut in serial section, and stained 
with haematoxylin and eosin. 
