1900] MICROSCOPICAL JOURNAL. 39 



sides of the lower plate upwards at four points ou the cir. 

 cumference so as to form pillars for supportiug the cover, 

 thereby allowing a complete circulation of air. It has 

 been found that the bacteria counts obtained by using 

 these ventilated dishes in an atmosphere saturated with 

 moisture, compare closely with those obtained in open 

 dishes protected from contamination and incubated in a 

 saturated atmosphere, the results of one series of com- 

 parisons giving 97 and 95 bacteria per cc, respectively, 

 by the two methods. Experiments have shown that 

 there is no danger of these ventilated plates becoming 

 contaminated from the air. 



The cultivation of water bacteria in the moist atmos- 

 phere has the further advantage that the growths come 

 to maturity in a shorter time. Liquefaction takes place 

 earlier, but the growth of the deep-seated colonies seems 

 to proceed at a still more rapid rate. A greater propor- 

 tion of the plates are liquefied a^ter 72 hours' growth, but 

 on the other hand, the percentage increase between the 

 48-hour count and the 72-hour count is much reduced. 



Incubators used for the cultivation of water bacteria 

 should be well ventilated, and their atmosphere should 

 be kept at or near the point of saturation. They should 

 be provided with wet and dry bulb thermometers, and the 

 relative humidity should not be allowed to fall below 95 

 percent. Experiuce has shown that an atmosphere practi- 

 cally saturated with moisture may be easily maintained. 



Clean Away Balsam. — To remove an excess of balsam 

 from around a cover-glass, allow the balsam to become 

 hard and then chip it away with the edge ot a blunt knife, 

 taking care to avoid touching the cover-glass during the 

 operation. A tooth brush dipped in methylated spirits 

 will then readily remove what is left. Finally, dry and 

 polish the slide with Japanese filter paper. 



