INTRODUCTION 29 



and commercial moment, and his contributions to our 

 understanding of infection, transmission and induced 

 immunity from disease, justify the statement that he was 

 easily our broadest minded and most comprehensive con- 

 tributor to the field of microbiology. 1 



Simple and natural as all this may seem to us now, the 

 stage to which the subject had developed when these obser- 

 vations were recorded did not admit of their meeting with 

 unconditional acceptance. The only strong argument in 

 favor of the etiological relation of the organisms that had 

 been seen to the diseases with which they were associated 

 was the constancy of this association and the occasional 

 transmission of the disease from a sick to a well animal by 

 the use of body fluids or bits of diseased tissue. No efforts 

 had been made to isolate them, and but few to reproduce the 

 pathological conditions by inoculation. Moreover, not a 

 small number of investigators were skeptical as to the 

 importance of such demonstrations; many claimed that 

 microorganisms were normally present in the blood and 

 tissues of the body; and some even urged that the organisms 

 seen in diseased conditions were the result rather than the 

 cause of the maladies. It is hardly necessary to do more 

 than say that both of these views were purely speculative, 

 and have never had a single reliable experimental argument 

 in their favor. Billroth and Tiegel, who held to the former 

 opinion, did endeavor to prove their position through experi- 

 mental means; but the methods employed by them were of 

 such an untrustworthy nature that the fallacy of deductions 

 drawn from them was very quickly made manifest by subse- 

 quent investigators. Their method for demonstrating the 



1 See Life of Pasteur, by Vallery-Radot. 



