112 PHOTOGRAPHING BACTERIA. 



up and out of the \vay and allow the operator to manipulate the microscope 

 before attaching 1 the camera. The bellows has an extension of two feet, 

 measured from the eyepiece of the microscope to the focussing screen. This, 

 with a two-millimeter objective and projection ocular 4, gives an amplifica- 

 tion of one thousand diameters. With less extension of bellows and lower 

 objectives amplifications ranging down to ten diameters may be obtained. 

 In focussing, the operator can, by standing 1 , observe the image on the screen 

 with a focussing 1 glass and manipulate the fine adjustment of the microscope 

 with his hand without using- a focussing' rod, though a suitable focussing rod 

 can be easily fastened to the camera upright if desired. 



Setting Up the Apparatus. The camera being hung 011 the rack-work 

 the microscope is placed beneath it, a stage micrometer is placed on the stage 

 and a medium-power objective and eyepiece attached to the microscope. 

 Light is reflected from the lantern upon the object by the mirror of the 

 microscope, the observer accurately centres the micrometer, then removing 

 the working 1 eyepiece a projection ocular is inserted, the camera racked 

 down, and with the image of the micrometer projected on the camera screen 

 the microscope is moved in such position that the centre of the micrometer 

 image is exactly in the centre of the screen. This position of the microscope 

 is marked once for all, and whenever afterward the microscope is placed in 

 the same place the centre of the object will be projected on the centre of the 

 screen. To correctly place the lantern, a lower-power objective is used, to- 

 gether with a high-power (Abbe) condenser. The objective is accurately 

 focussed on the lines of the stage micrometer; by adjusting the substage con- 

 denser a clear image of the lamp flame is projected on the plane of the ob- 

 ject (micrometer) and the lantern is moved to such position that the image 

 will be central. If the camera is attached, the image will appear central 

 on the focussing screen. 



This position of the lantern, like that of the microscope, should be fixed. 



To Photograph. In photographing- by oil light with all but the lowest 

 powers some form of substage condenser is necessary. This is due to the fact 

 that the source of light must always be focussed on the object in order to give 

 proper definition. In working with the objectives of four millimetres or 

 lower, it will be found advantageous to use objectives of lower power as 

 substage condensers, for it will be found that if placed in the substage for 

 ordinary work they greatly improve the definition of objects. In fact it may 

 be laid down as a general rule that whatever with a given light gives the 

 best definition to the observer's eye will give the sharpest photographic image. 

 Consequently, in high-power work where a condenser is used it will seldom 

 be necessary to change the microscope attachments when a photograph has 

 to be taken ; for in bacteriological work the Abbe condenser which gives 

 good definition will, when properly adjusted, give good photographic defi- 

 nition also, statements to the contrary notwithstanding. 



To photograph, place the microscope and lantern in position, light the 

 centre wick of the lamp, place a ground glass between the lamp and camera, 

 and focus the objective accurately on the object. The ground glass is used 

 only to reduce the light which might otherwise injure the observer's eye. 



The ground glass is then removed, a fine wire screen placed close against 

 the front of the lantern condenser, and by means of the substage condenser 

 an image of the screen is projected accurately on the object. This is very 

 important, for it is necessary that the light should be accurately focussed on 

 the object in order to produce sharp definition. After focussing the light, the 

 screen is removed and an opal glass is put in its place. On looking through 

 the eyepiece a clear sharp image of the object will be seen. If an Abbe con- 

 denser is used the iris diaphragm of the condenser should now be carefully 

 opened and closed until such an aperture is obtained that to the observer's 

 eye the object appears to the best advantage. The opal glass is now removed, 

 the camera attached to the microscope, and the projected image focussed on 

 the camera screen, preparatory to exposure. 



