30 NOTES ON MICRO-ORGANISMS. 
out till it is calculated that a single drop contains a few organisms 
only. This drop is then sown with necessary precautions, and 
may give rise to a pure culture straight away. If not, the process 
is repeated with the new culture. 
Continuous observation may be made by inoculating, with a 
needle or platinum wire, thin films of gelatine on glass slips, or 
in specially contrived glass chambers made of pieces cemented 
together with Canada Balsam or Coaguline. 
Marked peculiarities are met with at times in gelatine cultiva- 
tions; for instance, the formation of gas bubbles, usually of 
lenticular shape, but varying according to the density of the 
gelatine. In these cases a large volume of gas is occasionally 
developed by quite a slight growth of the organism, which is 
generally a very minute one. Spherical or pear-shaped liquid 
cavities are also formed, whose contents are usually acid. Some 
time ago I obtained a very nice growth of Bacillus ulna from 
such a cavity, the largest Bacterium I have yet seen. It was at 
least three times the diameter of Bacillus subtilis, and showed 
an active movement. 
A greatly improved definition under the microscope, of the 
membranes and cell divisions of micro-organisms, is obtained by 
staining with certain dyes; a process very elaborately described 
in Crookshank’s recent work on Bacteriology. I have tried 
staining with some of the aniline dyes in the following ways, 
which yield results quite good enough for ordinary examinations : 
Two or three drops of the liquid are placed on a glass slip, with 
sufficient space between them. They are then dried off gradually 
on a copper plate at a temperature of about i100 degrees 
Fahrenheit; a drop of very dilute Rosaniline or Methyl violet 
is put on to each of the dried spots, and evaporated to dryness 
as before. The surplus dye can be removed with very weak 
alcohol or very dilute nitric acid. These last are washed away 
with a little water, the slides dried off, and a little clove oil can 
be put on the spots, followed by Canada balsam. If the slide 
is wanted for immediate examination, it is unnecessary to remove 
the surplus dye; a little turpentine, followed by clove oil, will 
