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organisms ; by this, and by no other method with which 

 I am acquainted, it may be unhesitatingly affirmed that 

 the effect induced in a healthy animal by inoculation 

 with the tenth, twentieth, or fiftieth culture must be 

 ascribed not only to bacteria, but to the direct descend- 

 ants of those bacteria contained in the animal from 

 which the first cultures were made. And permit me to 

 add that after such demonstration has been furnished in 

 scores of repetitions with identical results, by indepen- 

 dent competent observers, by every one indeed, who has 

 attempted it, it is unwise and unreasonable, to put it 

 mildly, for any of us to deny, oppose, ignore, scoff at, or 

 equivocate about a fact established far more firmly than 

 are the majority of accepted facts, so called, in the science 

 and art of medicine. 



A consideration of importance in estimating the value 

 of observations upon bacteria, is the microscopical tech- 

 nique employed by the observer. That good objectives 

 should be used is well understood ; but it is now essen- 

 tial also, in delicate investigations, to employ a condenser 

 made after the pattern of Abbe's illuminator. The 

 feature which makes this apparatus invaluable in the 

 detection of bacteria is the possibility of 'obliterating, 

 through the large aperture of the lenses, the picture of 

 the object due to refraction, thus practically eliminating 

 from the field of vision everything which is not colored. 

 Bacteria not only absorb coloring matter aniline dyes. 

 for instance but retain these pigments in the presence 

 of reagents which decolorize the animal tissues, generally 

 speaking. To detect a minute organism, the bacillus 

 tuberculosis, for example, amid the cells, fibres, and gran- 

 ules of lung-tissue is, with ordinary illumination, ex- 

 tremely difficult or impossible ; but after decolorizing the 

 tissue and then, by means of the illuminator, obliterating 

 refraction outlines, the bacilli appear almost alone, by 

 virtue of their retained color, in a luminous field distinct 

 and easily recognizable. When, therefore, an observer 

 asserts the absence of all bacteria from a tissue tuber- 

 culous or leprous, for example usually supposed to con- 



