ON SOME NEW MICRO-ORGANISMS OBTAINED PROM AIR. 
261 
poured out upon a sterile glass-plate and allowed to congeal. Sometimes even a 
further attenuation is prepared by inoculating from the second test-tube into a third, 
which is also poured out upon a plate. 
In this manner one or other or both of the plates is almost sure to yield colonies 
sufficiently separated from each other to prevent interference and to enable further 
inoculations to be made from a single colony. 
By means of this method of plate-cultivation we have also controlled the purity of 
all our other cultivations. For, on submitting the contents of any culture-tube to 
plate-cultivation in this manner, any impurity in the original culture will become 
apparent through the production of dissimilar colonies on the plate. 
The colonies are also of great importance for the preparation of cover-glasses (see 
later below) for microscopic examination with a high power (1,000 diameters), as all 
the forms obtained from a single colony may with certainty be known to belong to a 
single organism. 
We must point out the great necessity of fully describing the appearance of all 
organisms when growing in colonies, as this forms one of the most important aids in 
the discrimination and identification of organisms. 
Microscopic examination ,—In addition to the macroscopic observations already 
referred to, we have examined, measured, described, and drawn all the various 
organisms as they appear when viewed under a high power of the microscope. For 
this purpose we have, in general, employed a oil-immersion (Leitz) objective, with a 
No. 3 eye-piece, thus obtaining a magnifying power of nearly 1,000 diameters, whilst 
for the examination of micrococci we have also employed Leitz’s -y 0 - objective, with 
the same eye-piece, thus obtaining a magnifying power of about 1,500 diameters. 
The organisms have, in general, been prepared for examination according to the 
Koch-Loffler* method. Thus a small quantity of a cultivation is transferred, by 
means of a platinum needle, to a clean cover-glass, a small drop of sterilised distilled 
water is added, and the mixture is spread as thinly as possible over the glass with the 
aid of the platinum needle. A second cover-glass is now laid upon the first and then 
drawn off, each glass being now provided with a thin film of diluted cultivation. The 
two cover-glasses are laid down with their wet faces uppermost and allowed to become 
quite dry. One of the cover-glasses is then held by one corner with a pair of forceps 
and slowly passed three times through the flame of a Bunsen burner or spirit-lamp, 
the face bearing the film being held upwards. The dried and ignited specimen can 
then be preserved indefinitely before staining for examination. 
The specimen is stained by running a few drops of a diluted alcoholic solution of 
an aniline dye (gentian-violet, magenta, methylene blue, &c.) with a pipette upon the 
cover-glass, which is held with forceps by one corner and moved about so as to cause 
the colouring matter to flow evenly over every part of the film. The dye is allowed 
to remain on the glass for about one minute, the exact time beino’ varied according to 
* ‘ Die Methoden der Bakterien-Fcrsclmng,’ Hueppe, Wiesbaden, 1885, p. 42. 
