162 



BACTERIOLOGY. 



the microscope when it is in the long axis of the apparatus, so as to 

 make a light-tight combination. The opening which is filled in an 

 ordinary camera by the lens can be shut off by means of an internal 

 shutter, which is opened and closed by turning a screw at the side 

 of the camera. The dark-back is provided with plate-carriers, so 

 that either half, quarter, or lantern-size plates can be employed. It 

 will be found convenient to have two or more dark- backs, so that 

 several plates may be exposed without rearranging the light for 

 each exposure. 



Much more elaborate and expensive micro- photographic cameras 

 have been constructed by Zeiss, and also by Swift. The latter has 



FIG. 81. PHOTOGRAPH OF AN IMPRESSION PREPARATION. 



carried out a suggestion made by Pringle for a support at the 

 ocular end (Fig. 80). 



The Dark-room. In every bacteriological laboratory there should 

 be a developing room provided with shelves, gas, water-tap, and sink, 

 but these arrangements are not absolutely indispensable. All that 

 is essential is a room impervious to light ; and a closet or cupboard, 

 if it can be ventilated, will answer perfectly well, with a jug and 

 basin instead of the tap and sink. The steam-steriliser employed 

 in the preparation of nutrient media for cultivating bacteria, if not 

 required at the time for such purposes, may be filled to the brim 

 with water, and will form an excellent cistern and tap, while a pail, 

 or small sanitary bin, may be utilised as a sink. 



Various kinds of lamps are made for the dark-room, burning 



