of his chosen field as far as he wishes to carry 

 his hearers, and may readily gain momentum 

 as he sweeps from the glorious achievements 

 of one master to the next; but the student of a 

 science which in itself is scarcely out of its 

 pioneer days is much more sharply limited in 

 such a retrospect. 



The science with which most of us who 

 are here gathered have to do is hardly old 

 enough to have a past. True it is that much 

 valuable work has been done in the earlier 

 decades of the century just closed, or even 

 before, but as a scientific subject on a more or 

 less exact foundation, the past two or three 

 decades have given us nearly all the knowledge 

 we have. Previous to this there was no science 

 of bacteriology. The theories* and ideas then 

 accepted were not based in any large measure 

 upon scientific deductions made from closely 

 controlled experimental work, but were more 

 the result of hypothetical postulates, which 

 were often the outcome of merely polemical 

 disputes. 



The change which confronts the student of 

 to-day is great. Now he finds a large mass of 

 accumulated data, more or less completely or- 

 ganized, and the underlying principles in many 

 lines quite thoroughly marked out. The boun- 

 daries of the province have been more or less 

 sharply defined, and we are recognizing the 

 limitations of even the germ theory of disease, 



