i8 



There were no marked tissue changes, the blood contained 

 no Bacteria, and it was incapable of infecting other animals. 

 It was nothing but a case of simple chemical poisoning by the 

 Septine of Dr. Richardson. A mode of death so much 

 insisted on by some observers opposed to the Bacterial 

 Theory. If a smaller quantity, say one or two drops, were 

 injected, sometimes nothing whatever happened ; but when 

 the inoculation was successful the animal remained well for 

 the first twenty-four hours, and then a definite train of 

 symptoms set in, followed by death on from 40 — 60 hours. 

 On Post-Mortem examination nothing was found except 

 enlargement of the spleen ; but the blood from the heart was 

 able to communicate the disease to other animals. Koch 

 felt certain from this that Bacteria were present in the blood, 

 but could not by any means detect them until he employed 

 the condenser of Abbe, of which I have already spoken. 

 Using this instrument he was able to find, not all the 

 various kinds of Bacteria contained in the fluid injected, but 

 only one very small Bacillus, varying from the io,oooth to 

 the loooth m. m. in lengths, showing that out of all the 

 Bacterial forms introduced this alone had found a suitable 

 soil, and been propagated. He further showed that as long 

 as this Bacillus was present in the blood that blood was 

 inoculable ; but as soon as it disappeared the blood was inert. 

 He found also that although house mice could be easily in- 

 fected with blood taken from diseased members of their own 

 species, rabbits and field-mice were altogether impervious to 

 its influence. 



The experiments did not end here. In some of his inocu- 

 lations Koch discovered, not only the presence of the Bacillus 

 in the blood, but he detected, in addition, a Micrococcus 

 sometimes growing freely in the neighbourhood of the inocu- 

 lation. This Micrococcus produced a local gangrene, which 

 did not extend very far before the animal died from the more 

 general disease. For a long time he tried to separate these 

 organisms, but in vain. At last, instead of injecting the 

 blood of the house mouse into the field mouse, it occurred to 



