Securing Food 



35 



x 32" x 11", with a door (not shown in figure) and back made of double 

 glass panes with a 1 inch air space between them. The cabinet is con- 

 structed of wood and insulated with celotex; the inside is painted white. 

 Culture flasks are kept on wire shelves which rest on adjustable metal 

 supports. A clearance of not less than % inch be- 

 tween the edges of the shelves and the walls of the 

 cabinet provides for better circulation of air. The 

 upper shelf is occupied by the refrigeration unit (R) 

 separated from the rest of the cabinet by a metal sheet 

 which serves for collecting the condensation water, and 

 also as a protection to the cultures placed just below it 

 against excessive cold. The temperature is regulated 

 by the air switch (A) connected to the electric re- 

 frigeration machine (not shown in the diagram). To 

 facilitate circulation of air a small electric fan (F) 

 may be hooked up to the air switch. Experience 

 shows, however, that when the refrigeration unit is in 

 operation there is a sufficient circulation of air inside 

 stand for iiiumina- the box. The temperature differences in the flasks 

 tion of the diatom placed on various shelves do not exceed 2 C. and a 

 temperature of from 15 to 16 C. may easily be main- 

 tained in the cabinet when the room temperature does not exceed 22 ° C. 

 If necessary the refrigeration unit may be 

 disconnected and a heater, placed on the 

 bottom shelf, turned on. The heating 

 assembly consists of a small heater (H), 

 fan (F), relay (E), and metastatic tem- 

 perature controller (M). 



Equal illumination on both sides of the 

 cabinet is provided by 18 Mazda 25 watt 

 bulbs, mounted on two separate stands ~^ 

 (Fig. 35) made of iron pipes and pro- 

 vided with metal reflectors which are 

 placed 3 feet from the glass walls. Under 

 this constant, controlled illumination and 

 temperature, Nitzschia cultures grow bet- 

 ter and faster than when kept before the 

 laboratory window. 



In a study of the effect of intensity of 

 illumination on the growth of Biddulphta 

 mobiliensis and Carteria sp., Schreiber 

 (1927) used the following method (Fig. 

 36). Cultures kept in the box were 



Q 



n 



I T 



3^, 





Fig. 36. — The method of grow- 

 ing Nitzschia under artificial il- 

 lumination. After Schreiber. 

 O, screen made of oiled paper. 



