122 Transactions of the Society. 



distrusted alike by philosopher and pedant ; but Pasteur — whose 

 work on silk-worm diseases, flaeherie and pebrine, and whose 

 studies in fermenting wine and beer even now had become classical, 

 — stimulated by Lister's praise and Koch's work on the anthrax 

 bacillus, took up the tale and fully confirmed Koch's results. He 

 cultivated the anthrax bacillus through a hundred generations, and 

 with the final culture series produced typical anthrax. Once 

 started, this brilliant and pertinacious layman (non-medical) 

 stormed position after position. He isolated and differentiated 

 pathogenetic anaerobic micro-organisms ; determined the effects of 

 temperature upon bacteria ; noted the fact that chicken -cholera 

 virus gradually loses its virulence when left growing in an arti- 

 ficial medium over a long period ; that this modification may persist 

 for many successive culture generations ; and that the modified 

 culture serves as a protective vaccine against acute chicken-cholera 

 virus much as Edward Jenner's vaccinia protects against smallpox. 

 In the test-tube or in the flask he succeeded in producing vaccines 

 against chicken-cholera, against anthrax, and against certain 

 diseases of swine, and then gradually brought out the fact that a 

 modification of a virus into a vaccine could also be obtained by 

 passing these viruses through a succession of different animals — 

 modification by passage —a method that later served him so well in 

 his experiments on the production of a protective virus against 

 hydrophobia. At every stage of his work, except in that dealing 

 with rabies or hydrophobia, he checked his results by careful 

 microscopical observation, and the confidence thus gained in his 

 earlier studies enabled him to anticipate the results that he would 

 obtain in his hydrophobia investigations, although he was not able 

 to confirm them microscopically. It is sometimes said that the 

 Microscope can no longer be called to our aid in the elucidation of 

 the life-history of the minute ultra-microscopic organisms that are 

 supposed to produce disease ; but it may be adduced with- justice 

 that it has already provided so many analogies that men walk with 

 great assurance in paths that they know must lead to the goal 

 aimed at. Moreover, the Microscope in its perfected form now 

 gives shadow-pictures which, like those imagined by Plato, indicate 

 the presence of things unseen. 



Medicine, then, has advanced just as fast and as far as the 

 Microscoi e, and other instruments of precision have helped and 

 allowed. All Ehrlich's earlier work in tissue-staining, and the 

 affinity of certain colours for special structures, was based on ob- 

 servations made with the Microscope. Weigert carried on similar 

 studies on the histo chemical reactions obtained in the staining of 

 micro-organisms and of the central nervous system, and laid the 

 foundation for Koch's special stain for the tubercle bacillus, without 

 which, and the aid of powerful and well-corrected lenses, we should 

 still be carrying on a blindly ineffective campaign against tuber- 



