98 MICRO-ORGANISMS AND DISEASE. [CHAP. 



occasionally in the blood-vessels of dead animals, bacillus of 

 malignant oedema (Koch), &c. in which in the single 

 bacilli and in the chains and filaments, the size of the 

 elements varies from that of a cubical or spherical mass of 

 protoplasm to that of a cylinder or rod several times as long 

 as it is thick. In some species (e.g. tubercle-bacilli), the 

 elements are almost spherical. There are on the other hand 

 other species (e.g. bacillus amylobacter) where the elements 

 are always rods or cylinders. In these cases of short bacilli 

 it sometimes becomes difficult to say whether one has to 

 deal with bacilli or bacteria, but the growth of the bacilli 

 into leptothrix, and particularly their power of forming spores, 

 is decisive, although neither of these events may happen 

 owing to peculiar conditions. 



(b) Some bacilli (e.g. hay-bacillus, bacillus in common 

 putrefaction, bacillus growing on surfaces of putrefying 

 material and tissues, bacillus found in the abdominal organs 

 after putrefaction has set in, &c.), are possessed of a flagellum 

 at one end, and are therefore endowed with the power of 

 locomotion. Other species (e.g. anthrax- bacillus, bacillus of 

 malignant cedema) are without such power. But even in 

 the first case the power of locomotion is possessed by the 

 bacilli only when single or in short chains, not by the longer 

 chains or leptothrix. 



(f) Not all bacilli are capable of forming leptothrix-fila- 

 ments. 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 amylobacter, leprosy-bacillus, tubercle-bacillus, &c.), 

 generally do not form leptothrix. 



(d) There exists the greatest variety in reference to the 



