WHAT ARE BACTERIA ? 27 



other organisms such as the Leuconostpc mesenteroides, 

 which is not pathogenic, and the Actinomyces or Ray 

 fungus. It is rather a curious fact, as Friedlander pointed 

 out, that this gelatinous capsule is formed only under certain 

 conditions, and he noted that in the case of the bacillus 

 of pneumonia the capsule could not always be demonstrated ; 

 that it occurred in the bacilli found in the lung tissue or in 

 the prune juice sputum so characteristic of the disease, but 

 that it could not be made out in the organisms grown on 

 such cultivation media as peptonized beef jelly. In the case 

 of the Ray fungus or Actinomyces, the organism that causes 

 wooden-tongue or Actinomycosis in cattle, this swelling of 

 the capsule at one end of the organism and not at the other 

 gives rise to a very peculiar club-shaped appearance of the 

 threads, and as these are frequently arranged so that the 

 thin ends of the rods are grouped together, whilst the 

 swollen ends are placed at the periphery of the radius, a 

 most peculiar and characteristic radiate arrangement of 

 wedge or club-shaped rods is the result. In some cases 

 bacteria first divide and multiply whilst they are embedded 

 in this common gelatinous mass, and it is only after they 

 have undergone a certain development that each organism 

 becomes invested with its own capsule and is allowed to lead 

 an independent life. 



It appears that in most cases in which the organisms con- 

 tain natural colouring matter, it is deposited in the capsule 

 and not in the protoplasm itself, and that the red, magenta, 

 blue, and yellow colouring particles that are met with in 

 this position give rise to the naked eye colour that is seen 

 where large masses of these organisms are growing. The 

 beautiful brown that is seen in Crenothrix and Cladothrix, 

 not only in the capsule, but in the surrounding cultivation 

 medium, is due to the presence of oxide of iron which the 

 organism is able to separate from water, or from other 

 media in which that substance is held in suspension or com- 

 bination. 



The composition of the limiting or external membrane, 

 as already pointed out, varies somewhat in different organ- 

 isms ; in many cases it appears to consist merely of an 

 altered myco-protein, but in others, as, for example, in 

 Bacillus anthracis, it is composed of a material analogous 

 to the casein of plants, combined with a substance which 



