ESSAYS ON BACTERIOLOGY. 33 



troduced, it is possible that the bacteria of these dis- 

 eases may remain in obscurity. There are other diffi- 

 ciilties in the way of the investigations, some of which 

 have already been explained. The problems are not 

 as simple and easy of solution as some suppose ; and we 

 could hardly expect that, in the few years since mod- 

 ern bacteriology arose, the field would have been 

 swept clean and there remain no more undiscovered 

 territory. 



Turning noAV from this explanation, let us review 

 briefly out knowledge of the specific bacterial causes 

 of the infectious diseases, remembering that with some 

 the demonstration seems to be complete, with others 

 only a high degree of probability has been reached; 

 with many there is still a large element of uncer- 

 tainty. 



In making this summary I shall omit such facts as 

 are already commonly known, and shall divide the dis- 

 eases into several classes : 



First. Those of which it may be said that the ques- 

 tion of their bacterial origin is apparently settled. It 

 will, perhaps, be surprising to some that so few axe in- 

 cluded in this class. They are anthrax, tuberculosis, 

 glanders, suppuration, tetanus, erysipelas. Probably 

 more increase in knowledge has of late come in regard 

 to tetanus than any other of the diseases included in 

 this group. The mystery in regard to this grave af- 

 fection has apparently been cleared up. Kitasato has 

 succeeded in perfecting a method of producing pure 



