I70 MICRO-ORGANISMS AND DISEASE [cHAP. 



This power is possessed in an eminent degree by certain 

 species, such as the hay-bacillus, the anthrax-bacillus, the 

 bacillus of malignant oedema, the bacillus found on the 

 surface of the mucous membrane lining the cavity of the 

 mouth and tongue (leptothrix buccalis). Other bacilli {e.g. 

 bacillus coli, leprosy-bacillus, tubercle-bacillus, &c.) generally 

 do not, though exceptionally they do, form leptothrix. 



Different species show great differences in the thickness 

 of the bacilli, some being very fine, e.g. bacillus of mouse- 

 septicaemia, bacillus of influenza; others thick and plump — 

 bacillus amylobacter, bacillus megateriuni ; but it is also 

 noticed that the bacilli of the same species growing in 

 different culture media show in some cases considerable 

 differences in this respect, in one medium forming thin 

 bacilli, whereas in another medium the bacilli may be twice 

 and thrice the thickness. The same may even occur in the 

 same medium (see Fig. 41). 



Many bacilli and bacillus-filaments {e.g. hay-bacillus, an- 

 thrax-bacillus) degenerate on growing old, the protoplasmic 

 elements becoming granular and breaking down altogether 

 into debris. This may occur to single elements within .a 

 chain or leptothrix ; and then the corresponding part of the 

 sheath of the chain, owing to the subsequent disappearance 

 of the debris, becomes empty and devoid of protoplasm. 

 Longer or shorter portions of a chain or leptothrix may thus 

 degenerate and become deprived of protoplasm, the sheath 

 only persisting. These portions become at the same time 

 thicker, the sheath having swollen up. 



Another mode of degeneration consists in the elements 



and sheath curling up, swelling up, and ultimately breaking 



down into debris. According to Cohn,i bacilh do not form 



zoogloea in the same way as micrococcus and bacterium do. 



^ Bciti: s. Biologie d. Pflanzen, vol. ii. 



