HOW TO AVOID CONTAMINATIONS. 103 
THE MAKING AND TRANSFERENCE OF PURE CULTURES. 
In addition to what,has been said under Pathogenesis, the following suggestions 
may be of service to the beginner. 
For the making of plate cultures and for the transfer of organisms from one 
culture medium to another, select a still day and, if possible, a day when a gentle rain 
or snow is falling. This offers ideal conditions, since the earth is wet, the outside 
air has been washed free from dust, and there is no wind to stir up dust within the 
laboratory. A strict adherence to this rule is sometimes very inconvenient and it is 
Fig. 88.* 
not meant to be iron-clad. It is, however, of immenise service in keeping cultures 
free from contaminations, and those who propose to disregard it should remember 
that haste in the beginning of an experiment often leads to vexation and delay in 
the end, especially when the success of the experiment depends absolutely upon 
the purity of the culture. 
*F ic, 88—Soft rot of green cucumbers inoculated by needle-punctures from a pure culture of 
Bacillus carotovorus. ‘The only parts not softened are those through which the infected needle en- 
tered, i, e., the parts rubbed with mercuric-chloride water. In each a little button of tissue under 
the disinfected area did not decay. ‘The sound fruit at the right was punctured at the same time, 
but with a sterile needle. She cucumbers had been removed from the vine, but were not flabby. 
They were exposed after inoculation to the ordinary air of the laboratory. The photograph was 
made on the seventh day. About two-fifths natural size. 
