^92 



Scientific Proceedings, Royal Dublin Society. 



, We must make some assumptions as to the volume of the tumour beiug 

 dealt witli. 



(1) "We assume the tumour to be an oblate spheroicl,with diameter of 22 cms., 

 and we suppose the tube to be placed axially and centrally, and the rays 

 to be emitted normally to the axis of the cylinder. In this case the rnjs 

 travel 1 1 cms. in the tumour. This we take as equivalent to about I em. of 

 lead; an assumption which may considerably depart from the truth, but error 

 in which only involves the assumed dimensions of the tumour. 



The area of the curve from to TO cms. of lead (which represents the 



CMS. of Lead 



path in the moi'bid tissues) is about ll'S units, reckoning the squares into which 

 the area is divided in the figure as units of iouisation. Now, when a screen 

 is used, that part of the curve extending from to the ordinate proper to the 

 thickness of the screen is not involved, but the curve defining the iouisation 

 now commences at the ordinate proper to the thickness of the screen, and 

 extends to the right for a distance of 1 centimetre of lead, as before. In the 

 present case, tlieu, we find tlie area of the curve included between the 



