DEVELOPMENT AND SCOPE OF BACTERIOLOGY 3 



his train, but the astonishingly shallow impression which the acute 

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

 furnishes an excellent example of the futility of the most penetrating 

 speculation when unsupported by experimental data. 



The real advancement in the scientific development of the subject 

 was destined to be carried on along entirely different lines. In 1837, 

 Schwann, a botanist, showed that the yeasts, found in fermenting sub- 

 stances, were living beings, which bore a causal relationship to the proc- 

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

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

 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 proteid decomposition, 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 completely 

 master the field until after Pasteur had completed his classical studies 

 upon the fermentations occurring in beer and wine, yet the conception 

 of a " f ermentum vivum " aroused much speculation, and the attention 

 of physicians and scientists was attracted to the many analogies ex- 

 isting 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 fermenta- 

 tion. 



Nevertheless, the diligent search for microorganisms in relation to 

 various diseases which followed, led to few results, and the successes 

 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 controlled etiolog- 

 ical research, it was Henle who formulated the postulates of conserva- 

 tism, almost as rigid as the later postulates of Koch, requiring that 

 proof of the etiological relationship of a microorganism 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 car- 

 ried out. 



It was during this period also that one of the most fundamental 



