INTRODUCTION. 25 



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 accumu- 

 late and finally gain access to the tissues, with the occur- 

 rence of decomposition as a consequence. Their results 

 were thus explained after a manner analogous to that 

 employed 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 originates. (See page 18.) 



Under the most careful precautions, against which no 

 objection could be raised, the experiments of Billroth 

 and Tiegel were repeated by Pasteur, Burdon-Sanderson, 

 and Klebs, but with failure in each and 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 in- 

 vestigators in many important respects. The scientific 

 methods of analysis with which each and eveiy obscure 

 problem was met as it arose served at once to distinguish 

 the worker as a pioneer in this hitherto but partly culti- 

 vated domain. The outcome of these experiments was 

 the establishment of a foundation upon which bacteri- 

 ology of the future was to rest. He, for the first time, 

 demonstrated that distinct varieties of infection, as evi- 

 denced by anatomical changes, are due in many cases to 

 the activities of specific organisms, and that by proper 

 methods it is possible to isolate these organisms in pure 



