98 BACTERIAL DISEASES OF PLANTS 



series of screens, i.e., ground glass, orange glass or orange paper 

 and red glass. An opaque screen also should be provided and 

 all the screens should be counter-weighted to slide up and down 

 easily inside a window frame. There should be at least two 

 of these windows. Our room has three. Two are over the 

 developing shelf and a third is in the south wall between the 

 developing shelf and the loading shelf. 



The developing shelf should face the source of light at a 

 convenient height rather than receive its light from one side. 



The washing sink (1 foot deep) should be close to the de- 

 veloping shelf to avoid waste of time and on the other side of 

 it should be a roomy fixing shelf. By "roomy" I mean large 

 enough for several trays. 



The loading and fixing shelves and the developing table are 

 each 36 inches high. The loading and fixing shelves are 18 

 and 16 inches wide. The developing table is 20 inches wide and 

 the surface of this table consists of two removable frames of 

 slat-work. Under it is a shallow lead-lined sink sloping to the 

 left and emptying into the deep sink. The window-ledges are 

 8^-2 inches above the top of this table. 



There should be plenty of storage shelves in the dark-room 

 (under the fixing shelf and the developing shelf, and over them 

 also) for trays, bottles, beakers, graduates, etc. 



The loading shelf should be in the darkest part of the room, 

 i.e., as far away from the red lights as possible and behind the 

 door or labyrinth, so that there shall be a minimum of danger 

 from fogging when boxes of dry plates are opened. I open boxes 

 of dry plates, always, with the opaque screen drawn low over 

 the red light, especially if they are orthochromatic plates. 

 The washing and printing are best done in adjoining rooms 

 (see Fig. 61). Dark-rooms, like kitchens, are most convenient 

 if everything is handy; they should not, therefore, be very large, 

 and consequently some sort of ventilation becomes necessary, 

 especially if they are much used. In the top of our own room 

 I have inserted a hood in the bottom of which is placed an electric 

 fan which can be turned on at will and which rapidly pumps the 

 foul air out of the room, the fresh outside air flowing in through 



