DK. R. BAZIN 



205 



tube, and are watched through the two symmetrical slots in the 

 sleeve. Measurements are taken with the aid of a vernier and a 

 lens. The apparatus is calibrated with the aid of bacteria suspen- 

 sions of known numbers. 



The capillary tube should neither be too fine nor too coarse ; in 

 the former case the capillary might become clogged, in the latter 

 the precision of the measurement would be impaired. The dilution 



r^=^3=^ 



Flask and Graduated Stirrup and 

 Capillary Brass Sleeve Stopper 

 Tube with Slot 



Fig. 3. 



of the suspension must also be suitable, as a concentrated prepara- 

 tion would entirely fill the capillary. The distilled water used should 

 carefully be filtered, since a small particle, e.g., of cotton, would 

 stop the tube. In order to facilitate comparative determinations, a 

 standard tube containing a suspension of known titre, of particles 

 of known dimensions and density, should be used ; porphyrised 

 kaolin may serv^ for this purpose, after levigation and filtration. 



