PHILADELPHIA 
Centz's moaification of tDe milleM12cPKr= 
son Colonp Coutitins Apparatus 
This apparatus, for estimating the number of colonies of bacteria in Petri 
dishes, was specially designed by us for water and milk analyses, etc. 
No. 2556, the simpler form of this apparatus, is more compact and conve- 
nient than the Miller- McPherson counter, and there is no screw to adjust every 
time a dish is removed. The price also is much less, and colonies can be ex- 
amined by reflected light, or the apparatus can be used in the vertical position 
(when the dish contains no liquefying colonies or when there is no objection to 
them running) and the colonies counted by transmitted light. In any position^ 
the springfs (A) prevent any movement of the dish in its relation to the diagfram, 
A transparent dark-blue glass, or any other contrast background, can be employed. 
The cover is not removed from the dish, as in some other counting apparatuses. 
No. 2558, the more expensive form, is constructed in the same manner as the 
above, but is provided with an arrangement to permit inclination, rendering pro- 
tracted counts of numerous colonies less tedious to the bacteriologist. The colonies, 
with the apparatus in this position, can be examined either by reflected light when 
a black background (provided) is inserted immediately behind the dish, or by dif- 
fused and transmitted light from the tilting reflector, when a colorless transparent 
glass is inserted. The reflector is reversible, and is white on one side and dull- 
black on the other. 
The adjustable hinged screen at top is blackened, and serves to protect the 
eyes of the bacteriologist from the glare of diffused light from laboratory window. 
This apparatus is also intended for use in the horizontal position with black 
or dark-blue background. 
In any position it is impossible for the dish (no matter what its size or 
thickness) to slip from its position with regard to the etched diagram after 
having been clamped, and there is therefore no danger of error in estimations 
through double counting from this cause. 
The complete apparatus folds neady, and is about. the size of the Wolfhtigel's 
apparatus now generally employed. 
No. 2556 
Open, Showing Wolfhugel's 
Chart 
No. 2556 
Closed, Petri Dish in Place, Showing 
Lafar's Diagram 
87 
