ANTAGONISM AND ATTENUATION 31 



it is aided in its growth by B. prodigiosus. B. aceti is under certain 

 circumstances antagonistic to B. coli. 



In several of the reports of the late Sir Eichard Thome issued 

 from the Medical Department of the Local Government Board, we 

 have the record of a series of experiments performed by Dr Klein 

 upon the subject of the antagonisms of microbes. From this work it 

 is clearly demonstrated that whatever opposition one species affords 

 to another it is able to exercise by means of its poisonous properties. 

 These are of two kinds. There is, as is now widely known, the 

 poisonous product named the toxin, into which we shall have to 

 inquire in more detail at a later stage. There is also in many 

 species, as several workers have pointed out, a poisonous constituent, 

 or constituents, included in the body protoplasm of the bacillus, and 

 which he therefore terms the intracellular poison. Now, whilst the 

 former is different in every species, the latter may be a property 

 common to several species. Hence those having a similar intracellu- 

 lar poison are antagonistic to each other, each member of such a 

 group being unable to live in an environment of its own intracellular 

 poison. Further, it has been suggested that there are organisms 

 possessing only one poisonous property, namely, their toxin — for 

 example, the bacilli of Tetanus and Diphtheria — whilst there are 

 other species, as above, possessing a double poisonous property, an 

 intracellular poison and a toxin. In this latter class would be 

 included the bacilli of Anthrax and Tubercle. 



There can be no doubt that these complex biological properties 

 of association and antagonism, as well as the parasitic growth of 

 bacteria upon higher vegetables, are as yet little understood, and we 

 may be glad that any light is being shed upon them. In the 

 biological study of soil bacteria in particular may we expect in the 

 future to find examples of association, even as already there are signs 

 that this is so in certain pathogenic conditions. In the alimentary 

 canal, on the other hand, and in conditions where organic matter is 

 greatly predominating, we may expect to see further light on the 

 subject of antagonism. 



Attenuation of Virulence op Function. — It was pointed out 

 by some of the pioneer bacteriologists that the function of bacteria 

 suffered under certain circumstances a marked diminution in power. 

 Later workers found that such a change might be artificially pro- 

 duced. Pasteur introduced the first method, which was the simple 

 one of allowing cultures to grow old before sub-culturing. Obviously 

 a pure culture cannot last for ever. To maintain the species in 

 characteristic condition it is necessary frequently to sub-culture upon 

 fresh media. If this simple operation be postponed as long as 

 possible consistent with vitality and then performed, it will be found 

 that the sub-culture is attenuated, i.e., weakened. Another mode is 



