PHOTOGRAPHY OF BACTERIA. 155 



various colours, according to their relative light intensity, and thus 

 be rendered iso- or, what is now more commonly known as, ortho- 

 chroma ti-.-. 



APPARATUS AND MATERIAL. 



Micro-photographic Apparatus. As is well known, various forms 

 of apparatus have from time to time been recommended and em- 

 ployed by different workers. 



Many use the microscope in a vertical position, with the camera 

 superposed or fitted to the eye-piece end of the microscope tube ; 

 or the microscope tube may be screwed off from the body of the 

 microscope, and a pyramidal camera, adjusted in its place, the base of 

 the pyramid being represented by the ground glass screen. 



Others again prefer that the microscope and camera should be 

 arranged horizontally. 



In another form the ordinary microscope is dispensed with, the 

 objective, stage, and mirror are adapted to the front of the camera, 

 and provided with suitable arrangements for holding the object, 

 supporting the mirror, and adjusting the different parts. 



Lastly, the camera may be dispensed with, the operating-room, 

 which must be rendered impervious to light, taking its place, while 

 the image is projected and focussed upon a ground glass screen, 

 winch has a separate support.* 



The horizontal position affords greater stability than the vertical, 

 so that the former is to be preferred. The vertical model with the 

 camera fixed to the microscope is particularly to be avoided, as the 

 weight of the camera bears directly upon the microscope, and must 

 affect the fine adjustment, and any vibration in one part of the 

 apparatus is communicated throughout. 



The simplest apparatus consists of a camera fixed upon a base- 

 board four or five feet in length, upon which the microscope can be 

 clamped, and which carries also a lamp and a bull's-eye condenser 

 (Fig. 77). 



Simplicity and economy must always be borne in mind in 

 recommending any apparatus of this kind, for to insist upon the 

 necessity of a very elaborate apparatus, or a specially fitted- up room, 

 or that a special room should be built with windows facing in a 

 definite direction, will in most cases at once place photography beyond 

 the reach of those who might otherwise employ it. Yet to fulfil 



* For an excellent account of the forms of apparatus which have been 

 employed by different workers the reader is referred to the section on Micro- 

 photography in Beale's Horn tn icork with the Microx< 



