SEA-FISHERIES LABORATORY. 205 
sterile water in a third flask. In this way four dilutions 
are made. 
In Flask I—1 c.c. contains 0-1 part of a cockle. 
Be i ‘ 0-01 
ee 0-001 
ev . i 0-0001 
2? ‘ ) 
99 re) 
bP) 
| In actual practice it was found that two dilutions 
were sufficient, but when examiming a sample of cockles 
for the first time four shou!d be made. 
One c.c. of liquid from each flask was then taken and 
put into a Petri capsule. Neutral-red, bile-salt, lactose 
agar* had been previously melted, partially cooled, and 
then put into the incubator at a temperature of 42° C., 
the tubes standing in a large dish of water. One tubeful 
of the medium was then poured into each of the Petri 
capsules containing the cockle liquid, and the contents 
were rapidly mixed by slightly shaking and rotating the 
capsule. The latter were then allowed to cool, were 
inverted and incubated at 42° C. for 20 to 24 hours, at the 
most. After this period the plates were read and the 
crimson colonies were counted. Most of the latter grow 
in the deep and appear, from surface view, as little 
elliptically-shaped bodies. They are really lenticular in 
shape, for the colony grows in a direction perpendicular 
to the surface of the medium (in the direction of least 
resistance). Generally they are surrounded by a haze, 
which is fairly evident. All crimson colonies growing in 
the deep were counted. 
Two plates were always made from each dilution. 
Representative colonies from all the plates examined 
were then selected and sub-cultured on the surface of 
* Grinbaum and Hume, British Medical Journal, June 14, 1902. 
The medium employed was prepared in the Pathological Department, 
Liverpool University. 
