INTR OD UCTION. 25 



Decomposition did usually set in, and they accepted 

 this as proof of the accuracy of their view. Atten- 

 tion 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 originates. (See page 19.) 



Under the most careful precautions, against which 

 no objection could be raised, the experiments of Billroth 

 and Tiegel were repeated by Pasteur, Burdon-Sander- 

 son, 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 

 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 the worker as a pioneer in this hitherto but 

 partly cultivated domain. The outcome of these ex- 

 periments was the establishment of a foundation upon 

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

 the first time, demonstrated that distinct varieties of infec- 

 tion, as evidenced by anatomical changes, are due in many 

 cases to the activities of specific micro-organisms, and 



