TEXT-BOOK OF BACTERIOLOGY. 221 



deal with some quite different species. The cells grow to a gigantic 

 size, become unshapely, and present irregular contours. In partic- 

 ular it will often be noticed that the rods swell moderately in the 

 middle and take an appearance which at the first glance reminds 

 us of the shuttle-like forms of the clostridia. On closer examina- 

 tion, however, it will be found that there is nothing like spore- 

 formation at work. In the hanging drop the whole micro-organism 

 appears equally dull, slightly granulated, without any trace of a 

 special body existing 1 within it as apart from the rest. When we 

 stain the bacilli the only parts which could be taken for spores, 

 those gleaming grains at the poles of the club-shaped rods or the 

 central part of the clostridia, take the coloring matter particularly 

 well, thus giving the clearest evidence of their not possessing the 

 nature of spores. 



In fact, the sporulation proceeds in quite a different manner. It 

 is true that the rods widen out at the place where the spore de- 

 velops, but only to such a slight degree that it can often scarcely 

 be perceived. The spores large, brightly -gleaming bodies, gener- 

 ally somewhat lengthened and slightly flattened or bent at the 

 sides lie at the end of the rod-cell generally, rather eccentrically 

 nearer to the one or the other wall. After sporulation has been 

 accomplished the remainder of the bacillus quickly perishes, the 

 spore becomes free, and is then only covered by a tender film of 

 remaining protoplasm. 



The conditions of sporulation for the black-leg 1 bacillus are not 

 yet certainly known. According to Kitasato, it does not take 

 place in the living animals, but occurs in the dead body and in our 

 artificial cultures. The spores possess quite a high degree of re- 

 sisting power; in a dry state they retain their vitality a long- time: 

 against the influence of heat and chemical agents they also show 

 themselves very resistant. 



The bacillus is, as we have just seen, a strictly anaerobic micro- 

 organism, to which oxygen is as fatal as to the cedema bacillus; 

 it thrives at ordinary temperature, above 18 C., and still better 

 in the incubator. 



The staining is performed in the ordinary manner without diffi- 

 culty. Gram's method robs the cells of their color again. The 

 spores do not take the aqueous anilin solutions, but are capable of 

 double staining. 



In gelatin mixed with grape-sugar or other reducing agents, 

 the colonies develop in a few days and show themselves as round 

 masses with irregular borders, which liquefy the gelatin very 

 quickly. Under the microscope one sees a dark opaque centre sur- 



