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220                 PATHOGENIC BACTERIA.

Pawlowski was able to cultivate the bacillus upon
potato, but Sander, who found that it could be readily
grown upon various vegetable compounds, especially
upon acid potato mixed with glycerin, also found that
upon such compounds its virulence was constantly lost.

It has also been shown that the continued cultivation
of the tubercle bacillus upon such culture-media as
are appropriate so lessens its parasitic nature that in the

FIG. 63.—Bacillus tuberculosis : adhesive cover-glass preparation from a fourteen-
day-old blood-serum culture;   x 100 (Frankel and Pfeiffer).

course of time it can be induced to grow feebly upon the
ordinary agar-agar.

It is really surprising to note the extremely simple
compounds in which the tubercle bacillus can be grown.
Instead of requiring the most concentrated albuminous
media, as was once supposed, Proskauer and Beck have
shown that the organism can grow in non-albuminous
media containing asparagin, and that it can even be in-
duced to grow upon a mixture of commercial ammonium
carbonate, 0.35 per cent.; primary potassium phosphate,
0.15 per cent; magnesium sulphate, 0.25 per cent;
glycerin, 1.5 percent It was even found that tuberculin
was produced in this inorganic mixture.