TWENTY-FIVE YEARS OF BACTERIOLOGY 119 



the same variety of microbe could not later gain another 

 foothold. Time has not upheld this simple conception; 

 but when it was formulated the subject matter of bacteri- 

 ology was still too fragmentary and scanty to point to the 

 deeper underlying chemical and biological processes in- 

 volved. Indeed, nearly ten years elapsed until Behring's 

 discovery of antitoxic immunity brought about a revolu- 

 tion in the prevailing ideas and opened up new and fas- 

 cinating vistas of research. 



We have now reached the period at which the German 

 school of bacteriology, led by Robert Koch, has arisen 

 beside the French. Koch's career in science was meteoric. 

 From an inconspicuous country practitioner he became, 

 in the period beginning about 1880, the outstanding world 

 figure in bacteriology. But his greatest work was com- 

 pleted in relatively few years, although that of his pupils 

 has continued up to and is still potent at the present day. 

 It is informing to reflect that just as Davaine made the 

 first signal advance in the experimental inoculation of 

 disease with the anthrax bacillus, and Pasteur the first 

 dramatic demonstration of the practicability of protective 

 inoculation with bacterial cultures also with that bacillus, 

 Koch rose into fame through the study of its life history 

 by direct observation under the microscope. But Koch's 

 greater contribution to bacteriology consisted of a method 

 of cultivation so perfected that pure growths of bacterial 

 species were readily obtainable. The consequence was 

 that in a very brief period of years a whole host of patho- 

 genic bacteria or incitants of diseases of man and animals 

 was secured, among which were the highly important 

 bacilli of tuberculosis, cholera, typhoid fever, diphtheria, 

 tetanus, dysentery, plague, meningitis and many others. 



Up to the period we are now considering, all the dis- 

 eases of microbic origin thus far investigated successfully 

 belonged to the class in which the bacteria invaded the 

 blood and the internal organs. But now we are about to 

 learn of another kind of disease induced by a class of 



