682 PRESIDENT S ADDRESS, 



however were certainly not the cause of tubercle. After much 

 patient toil he found a germ not easy to see without being dyed, 

 and moreover one which would not take the ordinary stains. It 

 is a very slender rod, about half the length of a blood corpuscle, 

 that is, the one seven thousandth to one ten thousandth of an 

 inch, and about one twenty-five thousandth of an inch in breadth ; 

 it is very slow to propagate, and apparently perfectly motionless. 

 Koch stands out prominently for his careful experiments, so we 

 can with advantage follow him. He took some pure tuberculous 

 matter, placed it in prepared blood in flasks which had the tuber- 

 culous matter mixed with it ; none showed any trace of decompo- 

 sition when it was examined microscopically, but after several days 

 he noticed slight scales form on the otherwise unaltered blood. 

 He took some of this scaly material and placed it in other flasks 

 of blood ; after repeating this process several times so as to be 

 quite sure that he had only one kind of organism present he 

 injected and ingrafted the scaly material into some animals, all 

 of which became consumptive, and when they were examined, 

 tubercles were found in their body, and the tubercles contained 

 these little rods which we have' seen composed the scales in the 

 prepared blood, and which were present in the original animals 

 which supplied the tubercular matter. Hundreds of experiments 

 were executed, and we cannot but accept his conclusions. Man}' 

 other fevers have been within the last year or two demonstrated 

 with more or less accuracy to have definite organisms ; for 

 instance malaria, typhus, typhoid, and leprosy, have all of them 

 Bacillus or rod-like forms. Then of the spherical forms we have 

 the germs of Diptheria, hospital gangrene, puerperal fever, blood 

 poisoning, &c. So also Erysipelas, Scarlatina, Variola, Vaccina, 

 Mumps ; even Syphilis has its germ, which belongs to the spherical 

 forms (Coeco-hacterio). 



These organisms, simple as they are, all differ in some way, 

 either as regards size, method of propagation, activity of 

 movement, or readiness of being stained. Indeed, as we know 



