1895 - 96 .] Dr Macintyre on Rontgen X-Rays. 
141 
the fluorescence of the bulb by sparking outside of the tube across 
the terminals, and by different sounds produced by the interrupter. 
By gently heating with the spirit-lamp or Bunsen burner this 
difficulty disappears at once, and so a fairly constant source of 
x-rays may be maintained for a long period. 
In taking photographs of the deeper structures of the body, the 
following points are worthy of attention : — Firstly, penetration ; 
secondly, definition ; thirdly, the photography of structures in the 
body which may have other structures placed in front or behind 
them, but which we do not desire to photograph : in other words, 
the selection of any particular structure within the body, and the 
omission of others. With regard to penetration, all the tissues of 
the body absorb the rays in a greater or less extent. While the 
bones absorb more than others, and therefore give the most striking 
pictures of the shadows, the soft tissues also absorb some of the 
rays, and by a careful arrangement these may be made to appear 
on a photographic plate or fluorescent screen. The mere penetra- 
tion of tissue is not a difficult matter. With the apparatus above 
described, and a current giving 12 volts 17 amperes, and a selected 
Crooke’s tube, the rays were found capable of penetrating a door 4 
inches thick, and coated with lead colour on each side, and in 
sufficient quantity, after passing through the air for 14 feet, to 
cause fluorescence on a screen in the next room. Again, the rays 
are sufficiently powerful to pass through two human bodies, or 
through 1 8 inches thick of pine wood ; and the spine, ribs, and 
other deeper structures of the body may easily be shown on fluores- 
cent screens. The rays may be generated in such force as to pass 
through these bones, giving such slight contrast between them and 
the spaces around that the former disappear, and the whole screen 
becomes one fluorescent mass. It is obvious, therefore, that 
definition is of great importance. While it is true we have no 
method at present of focusing in the ordinary sense, that is no 
evidence of refraction nor true reflection, yet correct definition may 
be obtained in the following manner ; — If a piece of white paper be 
laid on a table, and a pencil held at a short distance from it, a 
shadow of the pencil will be got on the paper. The nearer the 
pencil is to the paper the sharper the image will be. If the pencil 
be now removed from the paper towards the source of light, the 
