BACILLUS OF TUBERCULOSIS. 269 
ous bacilli have been distributed over the surface of 
the culture medium, a rather uniform, thick, white 
layer, which subsequently requires a slightly yellowish 
tint, is developed; when the bacilli sown are few in 
number, or are associated in scattered groups, separate 
colonies are developed, which acquire considerable 
thickness and have more or less irregular outlines. 
Growth on Peptonized Veal or Beef Broth Containing 
5 per cent. of Glycerin. On these media the tubercle 
bacillus also grows readily if a very fresh thin film of 
growth from the glycerin agar is floated on the surface. - 
The latter of these media is used for the development of 
tuberculin. The small piece of pellicle removed from 
the previous culture continues to enlarge while it floats 
on the surface of the liquid, and in the course of three 
to six weeks covers it wholly as a single film, which on 
agitation is easily broken up and then settles on the 
bottom of the flask, where it ceases to develop further. 
The liquid remains clear, containing in solution the 
products formed by the growth of the bacillus, and is 
really a dilute crude tuberculin. A practical point of 
importance, if a quick growth is desired, is to remove 
for the new cultures a portion of the pellicle of a grow- 
ing bouillon culture, which is very thin and actively 
increasing. 
The Obtaining of Cultures of the Tubercle Bacillus from 
Sputa and Infected Materials for Diagnostic Purposes. 
As this is a matter of great and increasing importance, 
we will consider in detail the methods which have 
been successfully employed. Pure cultures can he ob- 
tained directly from tuberculous material; but as 
it is so difficult to get rid of the other bacteria 
which are almost always present, and which grow 
