212 BACTERIOLOGY 



from which we have not yet entirely emerged, possesses its own 

 peculiar perils. In meditating on the cosmos, the agile mind is 

 always tempted to fill in the gaps of knowledge with closely knit 

 reasonings or fantastic imagery. The imaginative man of science 

 still frequently finds himself beset with the temptation to erect 

 an unverifiable hypothesis into a dogma and defend it against all 

 comers. It is now fortunately a truism that a more humdrum and 

 plodding course has proved of greater efficacy in advancing natural 

 knowledge. Theories that stimulate to renewed observation and 

 experiment have been of the greatest service, but unverifiable specu- 

 lations have often been a barrier to further advancement. Meta- 

 physics tempered with polemic is not science, whatever be its 

 allurements. 



If the attainment of a rational position in public hygiene, com- 

 munity hygiene, or preventive medicine must, then, be regarded as 

 the main objective* point in the campaign against disease, it follows 

 that the part played by bacteriology in this advance will be an 

 important one. The relations of bacteriology to public hygiene are 

 fundamental. The etiology of many of the most widespread and 

 common diseases that afflict mankind is intelligible only through 

 the medium of bacteriologic data. The modes of ingress of the 

 invading micro-organisms, the manner of persistence of the micro- 

 organism in nature, the original source of the infectious material, 

 and all the varied possibilities of transmission and infection can be 

 apprehended only through the prosecution of detailed bacterio- 

 logic studies. It is only by this means that the weak point in the 

 chain of causation can be detected and the integrity of the vicious 

 circle attacked. Success will inevitably depend upon a thorough 

 understanding of the circumstances governing and accompanying 

 the initiation and consummation of the disease process. Yellow 

 fever cannot be suppressed by burning sulphur or by enforcing a 

 shot-gun quarantine; the bubonic plague is not to be combated by 

 denying its existence. 



In the warfare against the infectious diseases a rational public 

 hygiene is ready to avoid the mistake of beating the air. A prelim- 

 inary survey of the possibilities reveals several distinct types of dis- 

 ease; those that are practically extinct or far on the road to extinc- 

 tion in civilized communities, those that remain stationary, or decline 

 but slightly, and those that show a more or less consistent increase. 

 The economy of energy would suggest that it is not a far-sighted 

 policy for public hygiene to focus its endeavors exclusively upon those 

 diseases that are yielding naturally before the march of civilization. 

 The conditions under which civilized peoples live to-day are in them- 

 selves sufficient to render the foothold of many infectious dis- 

 eases most precarious. What nation now fears that typhus fever 



