BACTERIA AND DISEASE 265 



and causal bacillus of that disease. Improvements in the 

 microscope and in methods of cultivation (Koch's plate 

 method in particular) soon brought an army of zealous in- 

 vestigators into the field, and during the last twenty years 

 first this disease and then that have been traced to a bac- 

 terial origin. We may summarise the vast mass of histori- 

 cal, physiological, and pathological research extending from 

 1650 to 1898 in three great periods: the period of detection 

 of living, moving cells (Leeuwenhoek and others in the 

 seventeenth century) ; the period of the discovery of their 

 close relationship to fermentation and putrefaction (Spallan- 

 zani, Schulze, Schwann, in the eighteenth century); and, 

 thirdly, the period of appreciation of the role of bacteria in 

 the economy of nature and in the production of disease 

 (Tyndall, Pasteur, Lister, Koch, in the nineteenth). 



But we must look less cursorily at the growth of the idea 

 of bacteria causing disease. More than two hundred years 

 ago Robert Boyle (1627-91), the philosopher, who did so 

 much towards the foundation of the present Royal Society, 

 wrote a learned treatise on The Pathological Part of Physic, 

 He was one of the earliest scientists to declare that a re- 

 lationship existed between fermentation and disease. When 

 more accurate knowledge was attained respecting ferment- 

 ation, great advance was consequently made in the etiology 

 of disease. The preliminary discoveries of Fuchs and others 

 between 1840 and 1850 had relation to the existence in dis- 

 eased tissues of a large number of bacteria. But this was 

 no proof that such germs caused such diseases. It was not 

 till Davaine had inoculated healthy animals with bacilli from 

 the blood of an anthrax carcass, and had thus produced the 

 disease, that reliance could be placed upon that bacillus as 

 the vera causa of anthrax. Too much emphasis cannot be 

 laid upon this idea, that unless a certain organism produces 

 in healthy tissues the disease in question, it cannot be con- 

 sidered as proven that the particular organism is related to 



