154 PROGRESS IN RADIOGRAPH r. 



lap, give an image without a break; but, on the other hand, should 

 the fracture be reproduced from a point at right angles from the first 

 position, the break in the bone will show plainly. In other words, 

 taken from in front, the fracture will be hidden, if the ends overlap 

 in that position, while it will appear clearly if the fracture is radio- 

 graphed from the side, because the broken ends will then be one be- 

 side the other. 



These theoretical and experimental demonstrations determined 

 clearly the technique for this kind of radiography. It is: (1) To 

 take not one but two radiographs of every fracture or suspected frac- 

 ture, these radiographs to be taken at diiferent points about 90 degrees 

 apart; (2) to place the fractured bone as close as practicable to the 

 photographic plate, and the Crookes tube perpendicularly above as 

 far as possible from the fracture and thus avoid distortion. This 

 is the method of procedure which pbtains in all laboratories worthy 

 of the name, and radiographs taken in accordance with it give little 

 basis for the statements of the belittlers of the process. 



If the rays employed are not penetrating enough for the case in 

 hand, the imperfection of the image will be so great as to prevent the 

 suspected break being seen as it should, and if, on the contrary, the 

 rays be too penetrating, the sensitive plate will not produce a good 

 image. Too many interruptions in a given time for a given case 

 will destroy the shading of the image, and, reciprocally, the image will 

 be too feeble if the number of interruptions is insufficient. And each 

 case requires an appreciation of its peculiar factors of penetration 

 and quantity. I will not even mention the problems regarding the 

 sensitiveness of the emulsions for the plate, the thickness of the films, 

 the qualities and faults of the developers, fixers, printing papers, or 

 of the difficulties in developing and printing. 



You have already surmised, no doubt, from the points we have just 

 touched upon that mere ability to get an image does not constitute a 

 radiographer. A perfect knowledge of tlie geometric laws governing 

 the formation of shadows is indispensable; not a theoretical knowl- 

 edge, but a practical acquaintance which will enable one to operate 

 rationally and to interpret logically the images obtained under care- 

 fully observed conditions. Moreover, the skillful practitioner must 

 have a perfect knowledge of the forms and exact proportions of the 

 bones or other parts to be observed, so as to be able to recognize and 

 appreciate the almost inevital)le radiographic deformation, and to 

 distinguish it from real malformation in the parts themselves. 



Besides this exact knowledge of geometry and anatomy, the radio- 

 grapher must be a clever electrician to imderstand the complex phy- 

 sical phenomena which govern the formation of X rays in the 

 Crookes tubes. A Crookes tube emits X rays of greater or less pene- 

 tration in proportion to its state of vacuum, and according to the 



