28 
Proceedings of Boycd Society of Edinhurgh. [sess. 
On a New Apparatus for Counting Bacterial Colonies 
in Roll-Cultures. By J. Buchanan Young, M.B., 
B.Sc., Public Health Laboratory, University of Edinburgh. 
Communicated by Sir Douglas Maclagan. (With a Plate.) 
(Read February 6, 1893.) 
The apparatus which I have devised for the counting of bacterial 
colonies in roll-cultures, consists of a glass tube 15 centimetres long, 
the surface of which is divided by finely etched lines into square 
centimetres. The bore of this tube is such that the roll- culture 
tubes, which are of a uniform diameter, just slide without play 
within it. The ends of the tube are fitted into brass collars (Al, 
A2), which have inserted in them india-rubber rings (Bl, B2). 
These india-rubber rings serve to retain the culture tubes in position 
during the process of counting. One end of the apparatus is 
adapted for grasping ordinary roll-culture tubes, the other for fixing 
the thin stems of Roux’s tubes for anaerobic cultures. The count- 
ing tube is capable of being rotated within the split-collars (C,C) by 
means of the milled collar D, and the culture tube being grasped by 
one or other india-rubber ring is necessarily rotated along with the 
counting tube. E is a sheet of optical black glass, which forms a 
suitable background for showing up minute colonies. F is placed 
below one of two small pinching screws, which serve to adjust the 
larger rubber ring for slight differences in the diameters of different 
culture tubes. 
To allow of check-counting in case of suspected error, and for the 
easy localisation of any given colony or colonies, registering-marks 
are made on the culture tubes by means of the scratching diamond, 
or other suitable means. These are indicated on the sectional 
drawings by dotted lines. The mark in the longitudinal axis of the 
culture tube is, in practice, made to correspond with a specially 
marked longitudinal line on the counting tube, and that in the 
transverse axis is brought just to the outer edge of the brass collar 
Al, or A2, as the case may be. The contents of each longitudinal 
row of squares are counted seriatim, the counting tube being rotated 
