TEXT-BOOK OF BACTERIOLOGY. 339 



gelatin a flat, saucer-like hollow develops, with a distinctly glisten- 

 ing pigment of green fluorescence around it. Liquefaction progresses 

 gradually' and advances to the walls of the tube. At the same 

 time the chief mass of the bacterial growth sinks to the bottom in 

 thick, slimy threads, the layers at the top clear up, and a delicate, 

 yellowish-green film appears on the surface. The entire culture 

 glistens with a green glimmer visible at some distance. 



A moist, rather thick, yellowish growth is developed on agar- 

 agar. It imparts a greenish hue to the medium. 



On potatoes there is formed a yellowish-gteen and smeary 

 growth which imparts to its neighborhood a peculiar pigment, like 

 the bacilli of blue milk. 



This material is probably generated bj' the bacteria as a color- 

 less product, and becomes a real pigment only on contact with the 

 oxygen of the air, for which reason it is, for instance, only observed 

 at the free edges of the bandages. It is, according to the investi- 

 gations of Ledderhose, who calls it pyocyanin, an aromatic com- 

 pound, related to anthracene, crystallizable, and without pathogenic 

 properties. 



The bacilli themselves, however, and their excretions are un- 

 doubtedly injurious to animals. On injecting into the subcutaneous 

 cellular tissue of Guinea-pigs or rabbits about 1 c.cm. of a fresh 

 bouillon culture, there will develop from the point of injection a 

 rapidly progressing oedema and a purulent inflammation of the ad- 

 jacent parts causing death in a short time. The bacilli can be as- 

 certained in the affected parts, in the blood, and in all internal 

 organs. After an injection into the abdominal cavity a pronounced 

 purulent peritonitis arises, and the characteristic rods are again 

 found, at the places just mentioned, mostly in dense heaps. 



If we take smaller quantities of the infective fluid, purulent foci 

 ■will be formed with narrower limits, and no fatal termination 

 will ensue. Animals having overcome this invasion will now bear 

 doses otherwise positively fatal. An injection of sterilized cultures 

 will also accomplish such a protective inoculation, which may be 

 regarded as being a result of becoming accustomed to increasing 

 doses of a poisonous substance, although, perhaps, those processes, 

 too, may play a part which otherwise lead to artificial immunity. 



The pathogenic character of the Bac. pyocyaneus was, until re- 

 cently, unknown and has been ascertained only by the investiga- 

 tions of Ledderhose and several French investigators, such as 

 Charrin and Bouchard. The last two have also established the 

 significant fact (already mentioned) that an incipient anthrax in- 

 fection may be stopped and cured by aid of the pyocyaneus. 



