148 ESSAYS ON BACTERIOLOGY. 



pie logic. Tliey fall in with tlie advancing current of 

 opinion and conviction, and conscientiously obey its 

 impulses. But they cannot just tell why they are 

 where they are, or whither they and we are drifting. 

 Possibly some of us who have had much to say to 

 them about bacteriology have so frightened and con- 

 fused them that they are unable to see that, though 

 sometimes in the midst of foaming billows, they are 

 nevertheless floating on a clear and beautiful stream 

 of truth, and therefore need have nO' fear of their 

 destiny. They will in time see that ancient land- 

 marks are only for the time being somewhat obscured, 

 somewhat changed, by the new view. To such I 

 hope to say a helpful word, by showing the fact and 

 method of a harmony between bacteriology and clin- 

 ical medicine. 



And first a few words toward a mutual under- 

 standing: 



I am to deal with the non-bacterial factors in the 

 infectious diseases; yet I shall have something to say 

 about such things as numbers and virulence of bac- 

 teria as influencing infection. By the words "non- 

 bacterial factors" is therefore meant agencies other 

 than the mere presence of bacteria which influence 

 the development of the infectious diseases. 



As to the degree to which such factors influence 

 particular infections, and the degree of importance to 

 be attached to them in clinical medicine, I have not 



