DEVELOPMENT AND SCOPE OF BACTERIOLOGY 3 



established with the work of Plenciz and many others who followed 

 in his train, but the astonishingly slight impression which the acute 

 reasoning of these men left upon the medical thought of their day 

 is illustrative of the futility of the most penetrating speculation 

 when unsupported by experimental data. 



The real advancement in the scientific development of the subject 

 was achieved along entirely different lines. In 1837, Schwann, a 

 botanist, showed that the yeasts, found in fermenting substances, 

 were living beings, which bore a causal relationship to the process 

 of fermentation. At almost the same time, similar observations were 

 made by a French physicist, Cagniard-Latour. The opinions ad- 

 vanced by these men on the nature of fermentation aroused much 

 interest and discussion, since, at that time and for a long period 

 thereafter, fermentation was ascribed universally to protein decom- 

 position, a process which was entirely obscure but firmly believed to 

 be of a purely chemical nature. 



Although belief in the discovery of Schwann did not master the 

 field until after Pasteur had completed his classical studies upon the 

 fermentations occurring in beer and wine, yet the conception of a 

 "fermentum vivum" aroused much speculation, and the attention of 

 physicians and scientists was attracted to the many analogies exist- 

 ing between phenomena of fermentation and those of disease. 



The conception of such an analogy, however, was not a new 

 thought in the philosophy of the time. Long before Schwann and 

 Cagniard-Latour, the philosopher Robert Boyle, working in the 

 seventeenth century, had prophesied that the mystery of infectious 

 diseases would be solved by him who should succeed in elucidating 

 the nature of fermentation. 



Nevertheless, the diligent search for microorganisms in relation 

 to various diseases which followed led to few results, and the suc- 

 cesses which were attained were limited to the diseases caused by 

 some of the larger fungi, favus (1839), thrush (1839), and pityriasis 

 versicolor (1846). During this time of ardent but often poorly con- 

 trolled etiological research, it was Henle who formulated the postu- 

 lates of conservatism, almost as rigid as the later postulates of Koch, 

 requiring that proof of the etiological relationship of a microorgan- 

 ism to a disease could not be brought merely by finding it in a lesion 

 of the disease, but that constant presence in such lesions must be 

 proven and isolation and study of the microorganism away from the 

 diseased body must be carried out. 



