64 TEXT-BOOK OF BACTERIOLOGY. 



enabled to study the micro-organisms freed from the many adven- 

 titious circumstances of their existence. All the hindrances to in- 

 vestigation which had before existed in the intimate mutual i-ela- 

 tions between the bacteria and their natural nourishing soil were 

 swept away. We were even enabled to vary at pleasure and in 

 detail the conditions under which the bacteria were allowed to 

 develop, and by observing their behavior under the conditions thus 

 altered very valuable criteria were obtained. 



New, hitherto unknown peculiarities were discovered, and the 

 rich abundance of added facts made it possible to distinguish be- 

 tween clearly separate species formerly thought to be identical. 



The artificial breeding of bacteria has been of the highest im- 

 portance in enlightening us as to their agencj' in producing dis- 

 eases. Although from the regular occurrence of the same bacteria 

 in the same disease the former might be regarded as the probable 

 cause of the latter, and although this probability was raised to 

 something like certaintj' by transferring portions of diseased organ- 

 isms to a healthy one, which then developed the same form of dis- 

 ease and showed the same bacteria — while this experiment could 

 be successfully repeated through a whole series of cases, yet all 

 these demonstrations were open to sefious objections. 



The existence of a special kind of bacteria was granted when it 

 could no longer be denied, but the micrororganisms were not ac- 

 knowledged to be the direct cause of the morbid changes; they were 

 regarded merely as an accompaniment, a consequence of the disease, 

 as uninvited yet harmless guests, for whose development the path- 

 ological conditions had proved particularly suitable. The success- 

 ful inoculations were explained by the supposition that the disease 

 produced a specific organic pathogenic virus, with the power of re- 

 producing the affection and calling forth the same changes, in the 

 course of which the bacteria found their way into the soil thus 

 prepared for them. 



This view of the case could not be disproved till the parasites 

 had been entirely removed from the diseased organism and freed 

 from, all surroundings to which disease-producing influence could 

 be attributed — i.e., not till they had been bred in isolation under 

 artificial conditions, and then tested as to their pathogenic power. 

 Should it now be possible by their aid to generate the same symp- 

 toms, there could no longer remain a doubt that they and they 

 alone were the cause of those symptoms. 



This experiment has been performed with success repeatedly, 

 and it is to the breeding of bacteria that we owe the most import- 

 ant discoveries of recent times with regard to the origin and nature 



