214 BACTERIA. 



wire used to distribute the bacilli as widely as possible. The colonies in 

 some cases are relatively few in number, because only a few bacilli were 



? resent in the pulmonary tubercles, as the examination of sections shows. 

 n other cases the little colonies are much more numerous ; in many, as 

 especially after inoculation with the contents of cavities very rich in bacilli, 

 they soon coalesce and form a coherent membranous mass." 



From the cultivations so made other tubes were inoculated 

 by lifting off the small scales with a needle bent at right 

 angles, breaking the scale up somewhat so as to cover the 

 point of the needle with the bacilli, and then drawing it 

 along the surface of the solidified blood serum. At the end 

 of ten or eleven days there became visible to the naked 

 eye, and very much earlier if examined with a lens, a 

 regular thin superficial layer spreading along each side of 

 the track of the needle. This organism does not bring about 

 the slightest liquefaction of the blood serum ; the scales are 

 somewhat dry ; they are exceedingly thin, and spread only 

 over the surface, no growth making its appearance in the deeper 

 layers of the nutrient medium. Tubercle bacilli cultivated in 

 this manner through seventy generations still continue to 

 act on animals in the same way as the original or first 

 culture. Similarly the bacillus grows only on the surface of 

 a fluid, forming a very delicate, thin film, the organism being 

 essentially aerobic in its habit. The film growing on solidified 

 serum is loosely attached to the surface, and any fluid intro- 

 duced, however gently, floats off a considerable portion in 

 larger or smaller flakes, which do not break up, but gradually 

 sink to the bottom. Koch observed, from the behaviour of the 

 films when growing on the surface of fluids, or broken down 

 and introduced into fluid media, that the tubercle bacilli were 

 non-motile. He described the appearances of these colonies 

 under the microscope, and came to the conclusion that the 

 growth was perfectly characteristic, as compared with any 

 other organisms known up to that time. They have the 

 appearance of lines or short threads thrown into curves like 

 worms, or snakes, or flourishes of a pen, thinner or thicker 

 according to the age of the colony, each thread being com- 

 posed of a large number of individual bacilli, arranged with 

 their axes in the long axis of the thread, running parallel to 

 one another, but with a small space between each, these 

 being apparently occupied by some zooglcea medium. This 

 arrangement can be best brought out by pressing down a 



