ESSAYS ON BACTERIOLOGY. H 



ranted embellLsliments, that honestly ignorant men re- 

 fused to believe it. 



When we inqtiire why, aside from such abuses, this 

 rational and simple explanation of the infectious dis- 

 eases remained so long a mere theory, the answer, in 

 the light of present knowledge, is again not difficult. 

 "Knowledge is of things we see," and there were no 

 means of seeing these minute objects which, with so 

 much reason, were supposed to exist. It was only 

 after the microscope, the aid to vision, was so far per- 

 fected as to enable men to look upon bacteria that it 

 could be demonstrated that such things really existed. 

 And only after many years of gradual improvement of 

 this wonderful instrument was this obstacle to prog- 

 ress overcome. 



But to see bacteria in disease, even to prove by ob- 

 servation their constant presence, is not sufficient to 

 demonstrate their causative influence. It can at best 

 prove only that they are regularly associated with 

 abnormal processes in the body, and furnish strong 

 evidence that they are living beings. If now we will 

 go a step further and prove that they iire actually the 

 seeds of disease, we must do what the agriculturist 

 does. We must be able to handle these seeds, to sep- 

 arate them from one another, to sort out the different 

 varieties, to obtain these varieties in sufficient quan- 

 tity for experiment; we must be able to plant them, 

 follow their growth, and find out what that growth 

 will produce. We must, in a word, cultivate these 

 our disease seeds as the agriculturist does his. 



