27? BACTERIA. 



^mentioned, starchy materials, vegetable infusions, hay and 

 meat infusions, and even sterilized alkaline urine, may be used, 

 the only thing that appears to interfere with their growth being 

 an acid reaction. Even this, however, may be present to a 

 slight degree if other conditions are favourable ; for example, 

 the anthrax bacillus grows readily on potato, which gives a 

 slightly acid reaction. On gelatine plates colonies grow and 

 are visible to the naked eye, on the second or third day, as 

 small white points which gradually spread outwards, and as 

 they come to the surface cause a slight liquefaction of the 

 surrounding gelatine ; they are then seen as small white 

 masses with wavy margins lying in a clear space, formed by 

 the liquid gelatine. When examined under the low power 

 they appear as round dark-green points with an irregular 

 outline ; on the second or third day this irregularity, 

 becomes much more marked and, as Fliigge describes it, 

 when it reaches the surface of the gelatine " the dark 

 remnant of the deeply-placed colony can only be seen, in 

 the middle. Around this centre, however, there is a light- 

 brown or light-grey shimmering mass, which consists; of 

 numerous wavy, curling bundles, recalling the appearance of 

 locks of hair or snakes on the head of a Medusa. Ultimately, 

 individual threads, or bundles of threads, branch oif from 

 the irregular periphery, and grow over the gelatine iq various 

 directions. At the same time the gelatine is liquefied over a 

 small area ; the colonies, which have now a diameter of 2 

 to 4 mm., begin to float and break down at their margins, 

 under the action of the fluid formed." 



An exceedingly good method of obtaining a permanent record of the 

 appearance of these colonies, is to lower a cover glass on to one of them 

 and then to raise it carefully without sliding it over the surface, so as to 

 take an imprint "of the colony upon the glass; the surface of the' colony 

 adheres to the glass and a thin layer is removed. This, when stained 

 with fuchsine or methyl blue and mounted in Canada balsam, gives an 

 exceedingly faithful "impression" of the appearance of one of these masses. 



The puncture cultivations of the bacillus anthracis pre- 

 sent most characteristic appearances. Along the track of 

 the inoculating needle there appear delicate feathery rays,., 

 which pass for some distance into the gelatine ; small lateral ^ 

 rays are given off" from these, and the whole of the young : 

 growth has a peculiar feathery appearance. These rays are 

 always longer near the surface, and gradually become snorter . 



