ANTHRAX. 



193 



noted that in these the bacilli are present in very small numbers, or 

 altogether absent. The bacilli should be examined both unstained 

 and stained. The rods are straight or sometimes curved ; rigid and 

 motionless. They can be stained with a watery solution of any of 

 the aniline dyes, and are then seen to be composed of segments with 

 their extremities truncated at right angles ; between the segments 

 a clear linear space exists, which gives them a characteristic appear- 

 ance (Plate V., Fig. 1). By double staining, with Gram's method and 

 eosin, the rods are seen to consist of a membrane or hyaline sheath 

 with protoplasmic contents. 



Drop-cultures. A little of the blood from the spleen or heart 

 may be employed to inoculate sterilised broth or blood serunu 

 Several of these cultures should be prepared, and some of them 

 placed in the incubator, and examined at intervals of a few hours. 

 It will be observed that the rods grow into long homogeneous fila- 

 ments, which are twisted up in strands, and partly untwisted in long 

 and graceful curves. The filaments begin to swell, 

 become faintly granular, and bright, oval spores 

 develop (Plate 1). The cultures in the incubator 

 develop rapidly. A temperature of 30 to 37 C. 

 is the most favourable for spore-formation. The 

 spores are eventually set free, and by making 

 a fresh cultivation, or by injecting them into a 

 mouse or guinea-pig, they germinate again into 

 the characteristic bacilli, which in their turn 

 grow into filaments and spores. When the spore 

 germinates it swells, the envelope becomes jelly- 

 like, and gives way at one or other pole, and the 

 contents escape and grow into a rod. 



Test-tube Cultivations in Nutrient Gelatine. 

 Typically characteristic appearances are obtained 

 by inoculating a 5 to 8 per cent, nutrient gelatine. 

 A whitish line develops in the track of the inocu- 

 lating needle, and from it fine filaments spread out 

 in the surrounding medium (Fig. 93). The fila- F IG . 93. PURE CUL- 

 ments are more easily observed with a magnifying TIVATION OF BA- 

 glass. In a more solid nutrient gelatine the growth 

 appears only as a thick white thread. As lique- LATINE. 

 faction of the gelatine progresses, these appearances 

 gradually alter, and the growth subsides to the bottom of the 

 tube as a white flocculent mass. In exhausted culture- media, and 

 sometimes in the blood, filaments are seen in a state of degeneration. 



13 



