102 



liACTEKIOLOGY. 



the ruirroseope when it is in tlie loug axis of the iippura.tus, so as to 

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

 or(finary camera hy the lens can he shut off by means of an internal 

 shutter, which is opeiieil and closed ^>Y turning a screw at the side 

 of the camera. The dark-back is provided with plate-cai-riei's, so 

 that either half, quarter, or lantern-size i)lates can be employed. It 

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

 several plates may be exposed witliout rearj'anging the light for 

 each exposure. 



[Much moi'e elaborate and expiensive mioro-jjhotographic cameras 

 have l.ieen constructed l>y Zeiss, and .also )>y .Swift. The latter has 



Fk;. 81. — PnOTOGUArH op .\N I.MI'RESSION PEEP.Ut-iTIOX. 



carried out a suggestion made by Pringle for- a supp(jrt at tlie 

 ocular end (Fig. 80). 



The Darh-rooiii . — In every bacteriological laboratorv there should 

 be a developing room pro\'ided with shelves, gas, water-ta}>, and sink, 

 but the.se arrangements are not absolutely indispensable. All that 

 is essential is a room impervious to light ; and a clo.set or cupboard, 

 if it can be A'entilated, will answer perfectly well, with a jug and 

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

 in the pi'e[)aration of nutrient media foi' cultivating hactei-ia, if not 

 i-equired at the time for such j^urposes, may be filled to the brim 

 with water, and will form an excellent cistern and ta[i, w liile a pail, 

 or .small sanitary l>in, may be utilised as a .sink. 



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



