VI] GENERAL CHARACTERS OF BACTERIA 115 



brough pneumonia spinning round with great velocity with- 

 out much changing their place. One and the same bacillus 

 was noticed to spin round for five minutes without any 

 diminution in its velocity ; then this gradually lessened, and 

 ultimately, after further five minutes, the organism came to 

 rest. When a drop of broth was added the spinning round 

 commenced again with great vigour. Some mobile bacilli 

 show motility under a certain condition and not under 

 others ; others again show it under all conditions. Thus, 

 for instance, many individuals of the bacillus of the Middles- 

 brough pneumonia show active locomotion in specimens 

 made of gelatine and Agar cultures ; made of broth cultures 

 the motility of many individuals is observable only while 

 the broth cultures are of recent date — 24-48 hours old ; 

 later on only very few motile individuals are met with. 

 The loss of motihty may be and sometimes is due to 

 chemical by-products in the cultivation [see bacillus of 

 grouse disease and of pneumonia). Some species of motile 

 bacilli when growing on a solid medium are capable by 

 their locomotion of distributing themselves from a given 

 point rapidly over and through the medium — e.g., certain 

 species of bacilli known as proteus of Hauser, certain 

 species of the potato bacilli, &c. ; this phenomenon is 

 spoken of as " swarming,'' thus, when a colony of such 

 bacilli appears on gelatine. Agar mixture, or potato, 

 irregular streaks and lines and patches of the growth are 

 soon seen extending in different directions, this being due 

 to the swarming of the bacilli from the first colony and by 

 the establishment of new colonies by the former. There 

 exist great differences in this respect between different 

 species of motile bacteria, for while some species do not 

 swarm at all and their colonies on solid media remain 

 localised and more or less well defined, though they 



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