ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



1027 



To find out tlie lengtli of exposure, use a Warnerke's sensitometer, in 

 oonjunction with the table and directions in Mr. Bousfield's ' Guide to 

 Photomicrography.' " 



Photographing Series of Sections.* — Dr. W. His photographs serial 

 sections with a magnification of 10-20 diameters with the following appa- 

 ratus : — A toothed bar carries at its front end a plate with the photographic 

 objective Ob : a second plate, moved by a rack and provided with a central 

 aperture, serves as object-carrier T : the two plates arc united by bellows. 

 The source of light is an Argand burner B, movable along the toothed 

 stage. The light is concentrated by two plano-convex lenses L, with a 



Fw 245. 



diameter of 11*5 cm. and a focal distance of 8 cm. Diffuse light is avoided 

 by the tin case Gh, in one side of which a broad valve or door is situated, 

 in order to obtain access to the inclosed parts. The objectives used were 

 a Steinheil's antiplanatic of 12 cm. focal distance or an aplanatic of 14 cm. 

 The latter, though not so powerful as the former, gives a corrector and more 

 definite image. Instead of a camera, the wall of the dark chamber W is used 

 as a reception surface ; the latter is divided into two halves and fitted with 

 a door and shutter S. By means of S the light is thrown on or turned off 

 the sensitized paper. The apparatus rests on a board Br which can be 

 moved along the surface of the wooden stand G. This sufiices for rough 

 focusing. Finer focusing is obtained by moving the object-carrier T with 

 a screw. Exact focusing is made by turning the objective, which works in 

 a tube provided with a fine screw-thread. The sensitized paper is, if small, 

 fixed down by small pegs ; if large it must be fitted into a frame C, 

 fastened to the wall. The image is first focused on a piece of white paper 

 placed behind the glass plate of the frame, and, this done, the sensitized 

 paper is introduced while the shutter S is closed. The paper employed is 

 Eastman's silver bromide paper, which is sensitive enough to artificial light, 



» Arch. f. Anat. u. Physiol.— Anat. Abtlieil., 1887, pi'. 174-8 1 fig.). 



