CH.IX.] BACILLUS. 67 



There are a great many species of bacilli, differing from one 

 another (a) in the shape of the elements, (b) in motility, (c) in 

 the power of forming filaments or leptothrix, and particularly 

 (d) in the thickness and length of the elements. 



(a) There are some species of bacilli e.g. hay-bacillus, 

 anthrax-bacillus, bacillus of putrid blood, bacillus found 

 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 



Fir,. 35. HACILLVS SVBTIUS GROWN IN TCKK BRO-H. 



At 1, the elements are thickened. The preparation had been dried and stained 

 with anilin purple. 



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 putre- 

 faction, bacillus growing on surfaces of putrefying material 

 \nd tissues, bacillus found in the abdominal organs after 



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