270 



PEACTICAL PHOTO-MICBOGBAPHY 



or by varying the position of the supporting-rods, the light 

 coming from the illuminant A may be reflected at any required 

 angle on to either or both sides of the object ; or the illumination 

 may be by reflected or transmitted light, as required. No 

 direct light reaches the object from the illuminant owing to 

 the opaque screen which is interposed. A ground-glass screen 

 may be substituted for the opaque screen should directly 

 transmitted light be wanted. This arrangement has the great 



FIG. 74. Arrangement of Camera and Illuminant for Photographing Tule- 

 and Plate-cultures of Bacteria. 



advantage that while the angle of the light may be varied at 

 will, the illumination in certain cases may if required be 

 perfectly even from both sides ; that is, if the position of 

 the mirror in relation to the source of light is exactly the same 

 on either side, perfectly even illumination will be obtained. 

 The appliance may therefore be used even for copying diagrams, 

 which are simply placed on the opaque screen and the light 

 reflected on to it. Exactly the same conditions apply in 

 photographing plate-cultures, as these again have either opaque 

 or transparent colonies on them. The opaque ones, however, 



