1892-93.] Mr J. B. Young on Counting Bacterial Colonies. 29 
by means of the milled collar for this purpose. The number of 
colonies in each square is noted on a paper scheme having squares 
corresponding to those on the counter. When the contents of all 
the squares have been thus noted, the total is readily obtained. 
The apparatus at present in use is that of Von Esmarch, which 
does not permit of the whole contents of the tube being actually 
counted. This I consider a distinct disadvantage, as the colonies 
are never so uniformly distributed in the culture medium, that the 
counting of the colonies in a given area, or areas, and calculating 
therefrom, can give more than a rough approximation to the number 
actually present in any culture tube. It was the recognition of this 
defect, and a desire to some extent to overcome it, that led me to 
design the apparatus now described. 
The instrument just described is that which I originally designed. 
I found, however, in practice that special care in counting was neces- 
sary when minute colonies came on, or very near to, a longitudinal 
line. I have therefore found it better to do aw^ay with the longi- 
tudinal lines, only retaining one of these to act as the registering- 
mark, and as the starting and ending point in counting. 
To use the apparatus as now arranged, we count the number of 
colonies in the space between two adjacent lines for the whole 
circumference of the tube, starting at the longitudinal line — rotating 
the tube as we count — and ending when the line is again reached. 
Having noted the number of colonies in this space, we now proceed 
to the next, and so on seriatim until the whole tube has been 
counted. 
