ASSOCIATION OF ORGANISMS 29 



form (Gordon). The Klebs-Lofiler bacillus in its turn may be 

 greatly modified in morphology and pathogenicity by environment. 

 Nor is the change necessarily in descending order. Non-pathogenic 

 organisms may possibly become pathogenic. We do not know. 

 The subject is one full of difficulty in a transition period of knowledge 

 in any branch of science. But there is no reason to suppose that 

 bacteria are exceptional in nature and outside the influence of 

 natural selection ; and it is not improbable that the views of the early 

 bacteriologists will have to be very much revised, and that eventually 

 it will be found that many "species" of micro-organisms are in 

 reali ty varieties of a single species showing involution and pleomorphic 

 forms. At the same time it should be recognised that amongst the 

 lowliest forms of life specific distinctions are, as a rule, less definite, 

 and less permanent, than amongst forms of life much higher in the 

 organic scale. 



The Association of Organisms 



At a later stage we shall have an opportunity of discussing 

 Symbiosis and allied conditions. Here it is only necessary to draw 

 attention to a fact that is rapidly becoming of the first importance 

 in bacteriology. When species were first isolated in pure culture it 

 was found that they behaved very differently under varying 

 circumstances. This modification in function has been attributed to 

 differences of environment and physical conditions. Whilst it is true 

 that such external conditions must have a marked effect upon such 

 sensitive units of protoplasm as bacteria, it has recently been 

 proved that one great reason why modification occurs in pure 

 artificial cultures is that the species has been isolated from amongst 

 its colleagues and doomed to a separate existence. One of the most 

 abstruse problems in the immediate future of the science of bacteri- 

 ology is to learn what intrinsic characters there are in species or 

 individuals which act as a basis for the association of organisms for a 

 specific purpose. Some bacteria appear to be unable to perform their 

 ordinary role without the aid of others.* An example of such 

 association is well illustrated in the case of Tetanus, for it has been 

 shown that if the bacilli and spores of tetanus alone obtain entrance 

 to a wound the disease does not follow the same course as when with 

 the specific organism the lactic acid bacillus or the common 

 organisms of suppuration or putrefaction also gain entrance. There 

 is here evidently something gained by association. Again the viru- 



* The three different degrees of association have been expressed by the following 

 terms : Symbiosis, the co-operation for a mutual advantage, not obtained other- 

 wise ; metabiosis, where one organism prepares the way for another ; antibiosis 

 (antagonism of bacteria), where one of the two associated organisms is directly or 

 indirectly injuring the other. 



