PHOTOGRAPHING BACTERIA. 109 



DESCRIPTION OF APPARATUS FOR PHOTOMICROGRAPHY BY OIL 



LIGHT. 



The apparatus consists of a camera, hung- in a vertical position, of a 

 microscope with substage condensers, suitable objectives and projection 

 oculars, and a Laverne tri-wick, oil stereopticon with the projection objec- 

 tive removed. 



Tfie Light. After trying all kinds of lamps, I found that the best illu- 

 mination could be obtained by using a tri-wick stereopticon with the pro- 

 jection objective removed, the middle wick only being lighted. The large 

 four-inch condensers serve to concentrate the light, while the double lantern 

 body prevents the radiation of heat to the microscope and shuts off all radiat- 

 ing light. Consequently the microscope does not become heated, and if the 

 room is darkened the absence of extraneous light greatly aids in focussing on 

 the camera screen. The oil light itself is quite yellow and so nearly mono- 

 chromatic that with orthochromatic plates a color screen is seldom, if ever, 

 required. After experimenting by taking photographs with and without a 

 screen, I have found 110 particular difference in result even when photo- 

 graphing difficult bacteria, and now seldom use one. If a screen is used a 

 solution of bichromate of potash and sulphate of copper in dilute ammonia 

 water placed in a trough between the lantern and microscope gives excellent 

 results and does not materially lengthen the time of exposure. The lantern 

 is placed about twelve inches in front of the microscope and with its central 

 long axis in a plane which extends through the centre of the microscope 

 mirror, the substage condenser, the objective, ocular and centre of camera. 



Microscope. The microscope is used in the upright position. I have 

 used this position rather than the horizontal for several reasons. The 

 microscope is used on the work -table in an upright position, and in working 

 when an object is found which it is desired to photograph, the microscope 

 without changing adjustments has only to be carried to the photomicro- 

 graphic apparatus, placed in position, correct adjustments of light made, the 

 camera racked into contact and the exposure made. With a conveniently 

 placed dark room the whole operation will occupy but a few minutes. The 

 upright position is necessitated when liquid preparations, as colonies of 

 bacteria floating on liquefied gelatin, are to be photographed, or when the 

 microscope is used for clinical photomicrography, as in photographing uri- 

 nary deposits in urine, blood corpuscles in Thoma blood counter, etc. In 

 bacteriological work where the bacteria are stained on the coyer and after 

 mounting the balsam is not quite dry, the cover is apt to slip if the micro- 

 scope is used horizontally, but this does not occur with the microscope placed 

 vertically. The horizontal position and long extension of camera is neces- 

 sary for certain work, particularly where large pictures (i.e., over four 

 inches in diameter) have to be taken, or where it is desired to obtain high am- 

 plification by extension of camera rather than by high eyepiecing, or in 

 photographing test diatoms with very high amplifications. For practical 

 work, however, up to amplifications of one thousand diameters, and for 

 photographs for illustration or reproduction, which are seldom required of 

 over three and one-half or four inches in diameter, the upright position is 

 much to be preferred 011 account of its ease of application and its practical 

 advantages. 



Camera. The upright position of the microscope necessitates a similar 

 position for the camera. To allow easy working, the camera is hung on a 

 rack -work attached to a rigid upright. * The upright is placed to the right of 

 the microscope so that it will be out of the way while working. 



Both the upper and the lower ends of the camera are movable on the 

 rack-work. The upper end, which carries the screen and plate-holder, is 

 movable, in order that different amplifications within limits can be gotten 

 with the same objective. The lower end is movable that it may be racked 



