INTRODUCTION. 29 



Decomposition did usually set in, and they accepted 

 this as proof of the accuracy of their view. Attention 

 was, however, shortly called to the fact that in cooling 

 there was contraction of the paraffin, resulting usually 

 in the production of small rents and cracks in which 

 dust, and bacteria lodged upon it, could accumulate and 

 finally gain access to the tissues, with the occurrence of 

 decomposition as a consequence. Their results were 

 thus explained after a manner analogous to that em- 

 ployed by Spallanzani, in 1769, in demonstrating to 

 Treviranus the fallacy of the opinion held by him and 

 the accuracy of his own views, viz., that it was always 

 through the access of organisms from without that de- 

 composition primarily originated. (See page 22.) 



Under careful precautions, to which no objection 

 could be raised, the experiments of Billroth and Tiegel 

 were repeated by Pasteur, Burdon-Sanderson, and Klebs, 

 but with failure in every instance to demonstrate the 

 presence of bacteria in the healthy living tissues. 



The fundamental researches of Koch (1881) upon 

 pathogenic bacteria and their relation to the infectious 

 diseases of animals differed from those of preceding 

 investigators in many important respects. The scien- 

 tific methods of analysis with which each and every 

 obscure problem was met as it arose served at once to 

 distinguish him as a pioneer in this hitherto but imper- 

 fectly cultivated domain. The outcome of these inves- 

 tigations was the establishment of a foundation upon 

 which bacteriology of the future was to rest. He, for the 

 first time, demonstrated that distinct varieties of infection, 

 as evidenced by anatomical changes, are due in many 

 cases to the activities of specific micro-organisms, and 

 that by proper methods it is possible to isolate these 



