I5O BACTERIOLOGY. 



Fig. 27). By double staining (p. 47), 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 is employed to inoculate the liquid 

 medium, bouillon or blood serum. Several of 

 these cultures should be prepared, and some of 

 them placed in the incubator. Examined from 

 time to time it will then be observed that the rods 

 grow into long homogeneous filaments, which are 

 twisted up in strands, and then untwisted in long 

 and graceful curves. In a few hours they begin to 

 swell, become faintly granular, and finally, bright, 

 oval spores develop (Plate I., Fig. 28). The cul- 

 tures in the incubator develop rapidly, a tempera- 

 ture of 25 40 C. being most favourable for 

 the growth of the bacillus. The spores are 

 eventually set free, and by making a fresh cul- 

 tivation, or by injecting them into a mouse or 

 guinea-pig, they germinate again into the cha- 

 racteristic bacilli, which in their turn grow into 

 filaments and spores. When the spore germinates 

 it swells, the outer layer becomes jelly-like, and 

 giving way at one or other pole, the contents 

 escape and grow into a rod. With the precautions 

 previously described (p. 97) cultivations should 

 be established in nutrient gelatine, nutrient agar- 

 agar, and on sterilised potatoes. 



Test- tube- cultivations in nutrient gelatine. Typically 

 characteristic appearances are obtained by inocu- 



