326 DR. WILLIAM ROBERTS. 



regular intervals along the threads. Finally, the threads 

 broke down, and the oval bodies, which could be nothing 

 else than spores, were set free and sank to the more depend- 

 ing parts of the drop. If the supply of nutriment were then 

 exhausted, the process ended here, and the spores remained 

 permanently unchanged; but, if additional nourishment 

 were provided, the new spores were seen presently to elon- 

 gate into rods, exactly resembling those originally existing 

 in the blood or spleen. If the conditions were favorable, 

 the new rods, after a period of rapid multiplication, in their 

 turn entered on the formation of a new generation of threads 

 and a new generation of spores. 



The next point was to test the pathogenic activity of the 

 rods and spores cultivated in this artificial manner. This 

 was done by introducing minute quantities of the rods, or of 

 the spores alone, into a small incision made in the skin of a 

 mouse. Speedy death from splenic fever occurred in every 

 instance. Koch found, without exception, that, if the tested 

 material produced threads and spores in the incubator, it 

 also produced splenic fever when inoculated into the mouse; 

 and, on the contrary, if no such growth and development 

 took place in the incubator, the tested material produced no 

 effect when inoculated into the mouse. Proof could go no 

 further : the infection absolutely followed the specific organ- 

 ism ; it came with it, it went with it. These observations 

 were repeated with the strictest precautions at the Physio- 

 logical Institute at Breslau, under the eyes of Professor Cohn 

 and other competent observers, who fully corroborated their 

 exactness. 



The variable duration of the activity of the contagium of 

 splenic fever was now explained. Koch found that the rods 

 had only a comparatively fugitive vitality ; they lost their 

 infective power generally in a few days ; at the most, in 

 about five weeks. But the spores retained their infective 

 activity for an indefinite period, in spite of all kinds of mal- 

 treatment. They could be reduced to dust, wetted and dried 

 repeatedly, kept in putrefying liquids for weeks, and yet, at 

 the end of four years, they still displayed an undiminished 

 virulence. 



Cohn calls attention to the fact that the organism of 

 splenic fever is identical in form and development with the 

 B. suhtilis. The only difference he could detect between 

 them was, that the rods of B. anthracis are motionless, 

 while those of B. suhtilis exhibit movements. The figures 

 you see before you might be indifferently labelled B. subtilis 

 or B, mithracis, and yet one of these organisms is a harmless 



