476 Scientific Proceedings, Royal Dublin Society. 



The activity due to a point-charge of one niillicnrie at a distance of one 

 millimetre, with no screening except the glass of the emanation tube, is taken 

 as 1,000. 



A. Activity due to 10 mc. in a tube 15 mm. long inside a standard 

 serum needle. 



B. Activity due to 10 mc. uniformly distributed over 6 sq. cm., the 

 emanation tubes being attached to the bottom of the brass box, 3 mm. thick, 

 which is placed in contact with the skin. 



G. Activity due to 10 mc. uniformly distributed over 6 sq. cm., but with 

 the emanation tubes attached to lid of the box, leaving an air space of 5 mm. 

 between the tubes and the inner surface of the bottom of the box. 



D. Activity due to 10 mc. uniformly distributed over 100 sq. cm., the 

 tubes being placed as in C. 



General Conclusions. 



It is evident that the conditions specified under D could not be con- 

 veniently realized with a single application ; but a similar (though not an 

 identical) effect can be obtained by successive applications of the brass box, 

 covering all parts of the required area in succession for equivalent times. 

 The total dose of millicurie hours must then be used in arriving at the 

 resultant action. For example, if we take the figures in the table as 

 measuring the effect produced by a ten-millicurie-hour dose, the effect of a 

 total dose of 200-millieurie-hours uniformly distributed over 100 sq. cms. 

 would be 20 times the corresponding figure in column D. 



The following points may be noted from the above figitres: — 



(1) The very great activity of emanation in needles at moderate 



distances. 



(2) The great reduction in surface effect caused by increasing the 



distance of the capillaries from the skin. 



(3) The still greater reduction in surface effect due to increase of 



area. 



The effect of interposing material such as chamois between the applicator 

 and the skin is nearly, but not quite, obtained by measuring " a " from the 

 outer surface of the chamois, i.e. by treating the chamois as the outer layers 

 of tissue in the above table. Thus, with conditions B above and 1 mm. of 

 chamois interposed, the activity on the surface of the skin would be 1'12 

 instead of 1"24. This shows the effect of chamois in acting as a distance 

 piece. 



This is not quite accurate, as chamois, being much less dense than living 

 animal tissue, the increase in secondary radiation is much slower in it, so 



