Fig. 1. Blackening ol pliutographic paper by an eleetroii beam generated by a van de 

 Graaff generator under the conditions used for experiments in mice (A) and rats (B, C). The 

 beam enters from the top of the picture through a saddle-hke lead shield and penetrates a 



•o cm 



number of sheets of photographic paper clamped together (on left). The circular field is 

 in diameter and well-defined at the periphery. The radiation falls off sharply between the 9th 

 and 10th sheets of paper. On the right a single sheet of photographic paper was exposed in a 

 slot of a wax phantom at right angles to the beam under similar conditions: (A) over a field of 

 1 cm diameter to a beam of 0-7 MeV, (B) and (C) over a field of 2-5 cm diameter to a beam at 

 1-0 MeV. In (C) the upper edge of the paper is shaped to simulate the dorsal contour of a rat. 

 (Courtesy of Dr. J. W. Boag.) 



Fig. 2. Section through a lesion in the'dorsal skin of a C57BL mouse exposed over a 1 cm 

 field to a dose of 8.000 rads given', in 30 seconds at 0-7 MeV. 419 days before fixation. The 

 hyalinized central part of the lesion is seen on the right (cf. Fig. 3). Subepidermal blistering 

 extends peripherally over a dermal region in which the elastic fibres (e.f.) appear as distinct 

 clumps, and coincides in position with the blood vessels (v) above the panniculus carnosus 

 (p.c). Weigert's Elastica. X 40. 



