ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



113 



New Colony-Counter.* — L. S. Ross describes a new bacteria colony- 

 counter (figs. 31-33), of which a great feature is that the glass bear- 

 ing the ruled lines can be brought quite close to the growth, by 

 which a great source of error is eliminated. A glass disk ruled to square 

 centimetres is mounted on the end of a short barrel that moves freely by 



Fig. 31. 



screw-thread within a collar. A block similar to that used in the Barnes 

 dissecting Microscope has a metal circle on the top over the mirror, of 

 a size to hold the 100 mm. Petri dish ; a rim is on the circle to hold the 

 dish in position. Underneath the circle a mirror, or a black surface if 



Fig. 32. 



desired, is placed at an angle of 45 degrees. A sliding-post bearing a 

 jointed arm is set into the block, to hold the lens in counting. The 

 dish to be counted is set upon the circle, the cover is removed, and the 

 barrel is placed disk down inside the dish, the collar holding the barrel 

 resting upon the edge of the dish. 



The barrel is lowered through the 



* Journ App. Micr., v. (1902) pp. 1970-1 (3 figs,) 

 Feb. 18th, 190.1 



