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.