ESSAYS ON BACTERIOLOGY. 159 



And tliTis we" become impressed with a third truth: 

 that the virulence of the microbes plays an important 

 role, not only in the typical development of an infec- 

 tious disease, but in the violence of the local and gen- 

 eral disturbance. ' 



That personal immunity or susceptibility and vari- 

 ations in number and virulence of bacteria are often, 

 indeed usually, intricately combined is evident. So 

 true is this that the clinical evidence of the non-bac- 

 terial factors in infectious diseases is often difficult to 

 sift. We must turn to experiment upon animals for 

 a solution of many of the problems. The answer 

 which bacteriology has to give has, it is hoped, been 

 partly set forth. More might be said, but surely 

 enough has been brought out to show that clinical, 

 medicine and modern bacteriology are not and need 

 not be out of harm vny. And he who has a clear view 

 of both will be in no danger of being either a bacteria- 

 maniac or a bacteria-phobic. 



A word in conclusion, and a simple illustration and 

 analogy. The more closely these things are studied 

 the more clear does it become that w© have in bac- 

 teriology but another example of some very old 

 truths. 



There is an ancient parable which tells us that a 

 sower went forth to sow, and as he sowed some seed 

 fell by the wayside, some upon stony ground, and 

 some upon good soil, with the result that some failed 

 entirely, some grew but faintly, while some flourished. 

 In the simple and stately scriptural phrase is set forth 



