188 ROYAL SOCIETY OF CANADA 



Description of Plates. 



The accompanying illustrations refer to the case of the cavity in the 

 lung mentioned on page 174. By way of contrast, a similar photograph 

 of a healthy lung is given in Plate II. Both photographs are reduced 

 about two-thirds from the original negatives. The cavity in Plate I is 

 bounded above and below by the shadows of the ribs, and on the outer 

 side by the shadow of the scapula. On the inner side its margin is less 

 sharply defined. The cavity is shown by an extremely dense black patch 

 in the original negative, and remains white after most of the other detail 

 , has vanished in the printing. The differences of density in the negative 

 are. in fact, so great, that it is practically impossible to reproduce them 

 by any process of printing. In printing these negatives sufficiently to 

 show the cavit}', the fainter detail of the spinal column is wholly lost, 

 and, yet, the cavity is far less clearly shown than in the original. In 

 reducing the plaies it was necessar}^, first, to print them on ordinary 

 silver paper, then to obtain a reduced negative by the wet process, which 

 was printed on the zinc plate. Since it is possible to obtain X-ray nega- 

 tives of almost any degree of density, it is very likely that it will be 

 found possible to pi-int direct from the original negative in many cases, 

 and thus to avoid the excessive loss of detail incidental to repeated 

 copying. 



