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D. C. VAN DYKE, P. JANSSEN AND C. A. TOBIAS 



strain were used in the comparison of the radiosensitivity of various species. 

 During irradiation all animals were given light barbiturate anesthesia, and 

 their heads were firmly mounted in specially designed holders (Fig. 1 ) . Rigid 

 fixation of the heads of all animals was accomplished by the use of ear plugs 

 and a sharp pin into the gingiva and maxilla between the dorsal incisors. To 

 keep the level of barbiturate anesthesia light, it was necessary to use xylo- 

 caine anesthesia locally in the ear canals and gingiva of the monkeys and 

 rabbits. 



Proper anatomic positioning of the beam was insured by having an x-ray 

 souixe aligned with the path of the beam, so that a roentgenogram of the 



Fig. 1. During irradiation all animals were given light barbiturate anesthesia, and 

 their heads were firmly mounted in a specially designed holder. For proper positioning 

 of the beam, a "Land" camera was placed in the path of the beam beside the animal's 

 head. 



skull with the image of the alpha particle beam superimposed could be 

 made for each animal. For this purpose a "Land" camera was placed in the 

 path of the beam beside the animal's head (Fig. 1). Figure 2 is such a 

 "Land" camera roentgenogram of a rat's skull with the image of the 2.0 X 

 25.5 mm beam superimposed. Such pictures served as a permanent record 

 for later comparison with the position of the band of fluorescence or the 

 position of miscroscopic changes. 



A 2.0 X 25.5 mm brass aperture 6 in. thick was used, except in the experi- 

 ment where the effect of aperture size was specifically studied. The distance 



