124 ESSAYS ON BACTERIOLOGY. 



comparatively easy, and tlie way opens for experi- 

 ments with it in the direction of diagnosis, prevention 

 and cure. 



It has already been pointed out that the explana- 

 tion of the disease-producing action of bacteria is to 

 be sought chiefly in their poisonous contents and 

 products. For the purpose of obtaining these poison- 

 ous products or toxins for experimental work, the bac- 

 teria, once obtained in pure cultures, axe usually 

 grown in liquids. The bacteria are then filtered out 

 by porcelain filters, leaving a fluid containing the 

 toxin, which, representing the active principles of the 

 bacteria, may, for experimental purposes, be used in 

 exact dosage. Or, to more fully imitate nature, the 

 bacteria themselves, washed free from all extraneous 

 substances, may be pulverized and dissolved to ob- 

 tain their constituents. Here again, while general 

 principles and methods are simple, the details of suc- 

 cessful work are often many and perplexing. But 

 such difficult procedures belong chiefly in the experi- 

 mental laboratory; the culture work available and 

 iiseful to the practicing physician, following, as it 

 does, the paths laid out by the investigators, once 

 learned, is uncomplicated and easy. 



The microscopic study of bacteria is an exceedingly 

 attractive stibject to the physician, revealing a world 

 of curious and interesting things, and opening up a 

 most valuable field of diagnosis. Improvements in 

 the construction and manipulation of the microscope 



