MORPHOLOGY 



523 



FIG. 252. Bacillus anthracis. Broth 

 Iture. 

 Reich.) 



The bacterial filaments are 1-2/x broad, very long, wavy, cylindrical, 

 flexible and fitting one within the other like the strands in a skein of silk. They 

 are squarely cut at the end, are never branched 

 and appear to be absolutely non-motile. 



R. Dupond has however noticed a very slow 

 and flexuous movement in a broth medium con- 

 timing no salt when examined on a warm stage at 

 38 C. After making several sub-cultures of the 

 first vaccine of the Institut Pasteur on glycerin- 

 sagar-agar he was able by staining to demonstrate 

 flagella arranged regularly around the bacilli. 



Staining methods. Like the bacillary form, 

 the filaments stain with the basic aniline 

 dyes (carbol-thionin is best) and are gram- 

 positive. 



When stained the filaments are seen to be ? ul ^ re - c ^boi-thionin. (Oc.ii.obj. 8, 

 made up of an hyaline sheath enclosing a 

 number of homogeneous protoplasmic segments separated one from another 

 by transverse partitions, each segment representing a cell which rapidly 

 forms a spore. 



(iii) Spores. 



To study the formation and development of spores it is necessary to 

 examine a hanging-drop preparation. The best method is to use a Koch's 

 cell ; place a drop of aqueous humour on the cover-glass and sow it with a 

 trace of anthrax blood. 



If the cell be kept at a temperature of 35-37 C. a small refractile point will 



appear within the protoplasm of the bacilli 

 in the course of a few hours. This point 

 increases in size and by reason of its re- 

 fractibility becomes a distinctly visible ovoid 

 body. The spore is the resistant form of 

 the bacillus. 



Spore formation only takes place under cer- 

 tain conditions : the presence of free oxygen 

 is essential and the cultures must be grown at 

 a temperature between 18 and 41*5 C. Above 

 42 C. spores are not formed. 



The protoplasm of the original bacillus 

 soon breaks up leaving the spore surrounded 

 merely by the delicate membrane which 

 enclosed the organism in its filamentous 



su. -uu^c/w/w-o wrvuii w/i>to. ajAVAiici. Q/ 1 j_l * * "1 " 1" 



method. TO demonstrate spores, x 925. iorm and this in turn disappears leaving 

 SS^ UrtiS> EssentMs of Practical Bac ~ the spore free. No one bacillus ever gives 



rise to more than one spore and this is 



always smaller than the mother cell ; some of the bacilli are sterile so that 

 a spore does not form in every cell of the chain. 



If the medium is sufficiently nutritive, the spore will soon begin to change 

 into a bacillus. It first increases in size and loses its refractibility, then the 

 enveloping membrane is absorbed leaving the protoplasm free, finally it 

 elongates and assumes the bacillary form (De Bary). 



Staining methods. The spores of anthrax may be stained by the methods 

 described in Chap. IX. It is difficult to stain the spores by the double 

 method, but if attempted absolute alcohol should be used for decolonization 

 and not acids (p. 147). 



FIG. 253. Bacillus anthracis. Holler's 



