210 BACTERIOLOGY 



grape-sugar to the agar. Pawlowsky found that white 

 detachable colonies appear on the surface of potatoes in 

 twelve to twenty days, but the potato discs must be pro- 

 tected from evaporation in air-tight glass tubes. The bacilli 

 grow in the most luxuriant manner, according to Koch, in 

 an infusion of veal rendered feebly alkaline, and to which 

 an addition of 4 or 5 per cent, glycerine and 1 per cent, 

 peptone has been made. Inoculation is done by floating 

 a fairly large piece of the seed-culture upon the surface of 

 the fluid, and when the cultivation has b^en kept for 

 several weeks in the incubator, the surface becomes covered 

 with a tolerably thick skin, dry above, and often wrinkled, 

 which a few weeks later becomes moistened by the fluid, 

 breaks up into single ragged pieces, and sinks to the 

 bottom. Growth requires from six to eight weeks for its 

 completion. 



With regard to the staining of tubercle bacilli, it is of 

 considerable importance, according to Koch, that the colour- 

 ing fluid should have an alkaline reaction, as these micro- 

 organisms will only take the aniline dyes when acted on 

 simultaneously by alkalies. In order to protect the ob- 

 server, Pampukes recommends that the tubercular sputa 

 should be sterilised at 120° C. before being examined, as 

 this does not impair their power of absorbing stain. 



For practical investigation, the observation of Dahme 

 is of importance, that the flakes which lie at the bottom of 

 the sputum contain the greatest number of bacilli (fig. 83). 



According to the method of Koch and Ehrlich, the 

 sputum to be examined is poured upon a dark surface, and 

 the tenacious yellowish particles are picked out. By 

 means of a penholder containing a nib one half of which 

 has been broken away the smallest possible lump of 



although identical in appearance and staining, they are now generally re- 

 garded as a distinct variety.] — Tk. 



