240 TRANSACTIONS OF THE [Sess. lxxviii. 



generally uses are the " Royal Standard " plates by Cadett 

 & Neall. 



Exposure. — The slide, when ready, is placed on the 

 stage and the microscope focussed. Great care must be 

 taken to adjust the mirror of the microscope so that the 

 field is perfectly uniformly illuminated ; for unless this 

 be carefully done the results will be disappointing. The 

 required portion of the section having been selected, the 

 camera is fixed to the microscope, and the focussing, ground- 

 glass screen placed in position. It will now be found 

 necessary to re-focus so as to have a clear image of the 

 section on the focussing screen. This done, the shutter of 

 the camera is closed, the dark slide slipped into position, 

 and the exposure made. The exposure should, for moder- 

 ately low magnification, last from two to five minutes, 

 according to circumstances, such as the transparency of the 

 section, intensity of the light, and so on. Immediately the 

 time of exposure has expired, and before closing the dark 

 slide, quickly but gently close down the shutter of the 

 camera. Then push in the sliding face of the dark slide 

 while the latter is still in position. Any modifications 

 necessary to meet special circumstances can, with a little 

 practice, be easily devised. 



Developing, Fixing, and Printing. — These operations 

 being precisely the same as in the case of ordinary photo- 

 graphy, the reader is referred for guidance to one of the 

 many cheap books now available on the subject. Suffice 

 it to say that, when printing, the part of the negative not 

 required for reproduction should be masked off. Masks 

 are sold by all dealers in photographic requisites in the 

 following two forms : (1) Those which are already cut to 

 shape, and (2) those which can be easily cut into any shape 

 and size. A curved pair of scissors is very useful for 

 cutting circular masks. The mask, when cut into shape, 

 should be stuck on by one corner to the film side of the 

 negative. By this means any number of precisely similar 

 prints can be obtained. 



Cost of Apparatus. — All that is absolutely necessary by 

 way of apparatus is included in the following list, with 

 approximate prices appended : — 



