fee 
XXX. 
ON A METHOD FOR COLOURING LANTERN SLIDES FOR 
SCIENTIFIC DIAGRAMS AND OTHER PURPOSES. By 
PROFESSOR J. A. SCOTT, M.D. 
[Read Marcu 21; Received for publication Marcu 30; Published Aprin 25, 1894. ] 
THe method of colouring the gelatine film with the anilin and 
other dyes is not new; butin the form in which it has been prac- 
tised hitherto, the dyes have been thickened and used on the sur- 
face after the manner of ordinary pigments. In the method which 
I have adopted, the gelatine is stained simply without the addition 
of any medium. In orderto make the colour run evenly, the 
gelatine film should be moist, but not wet with drops of water— 
the most favourable condition being immediately after the final 
washing of the slide is completed, and the film allowed to drain ; 
but if this should not be convenient, the slide may be placed in 
water for a quarter of an hour, and then drained. If the slide 
has been dry for some days or weeks, a greasy film appears on the 
surface, which should be removed with a little methylated spirit 
before soaking in water. 
In this damp condition the colour will be absorbed slowly and 
evenly, when a dilute solution of the dye is applied with a brush. 
The colours show no tendency torun. The intensity of colour 
depends primarily on the strength of the original solution, and 
secondly on the length of time it is allowed to act on the gelatine, 
so that local shading can be produced by keeping the brush in one 
spot fora longer time. Should the trial be unsatisfactory from 
any cause, the colour can be completely removed by soaking in 
clean water for some time, and the slide can be re-painted. 
If the colours are placed simply on the gelatine, almost any of 
the dyes can be used ; but some are more likely to fade than others, 
and a few are more easy to lay on evenly. If, however, the colours 
have to be mixed, either before painting or by overlapping on the 
gelatine, it is important to remember that some of the dyes act 
