92 



mice was infectious, and the disease conld be transmitted 

 from one mouse to another even with only the tenth of a drop 

 of blood. Koch carried this on through seventeen successive 

 inoculations, and always with the same results. He inferred 

 that the mice were killed by a micro-organism, but for a long 

 time his closest scrutiny failed to discover it. At last, after 

 prolonged search and the adoption of the mode of observation 

 I have previously described, he discovered in the blood of these 

 mice an immense number of bacilli, which were so minute as to 

 escape detection under all the ordinary modes of examination. 

 ■So long as these could be found in the blood, so long was the 

 blood infectious; but so soon as they disappeared the blood 

 could be injected into another animal without risk. And here 

 "we may notice a curious fact, which is probably true of all the 

 infective Bacteria — each species appears to have its own 

 favourite habitat. They flourish in some species of animals, 

 but die or have no effect in others. Thus Koch found that if 

 Tie inoculated a field mouse instead of a house mouse with 

 infected blood the animal was not susceptible. I am not 

 unmindful that objections have been frequently urged against 

 the conclusions drawn from experiments of this kind on the 

 ground that the Bacteria in these cases are the accidental 

 products of other changes, and not the cause of the abnormal 

 <3onditions in which they exist. I shall therefore bespeak 

 your patient attention to another infectious disease, in 

 which the life history of a rather large form of bacillus 

 has been so thoroughly worked out by Davaine and Pasteur 

 in Prance, Koch and others in G-ermany, and Klein in Eng- 

 land, as to leave no room for such objections. I refer to 

 a disease known under many names, but more commonly as 

 ■charbon anthrax, splenic fever, or malignant pustule. Long 

 before bacteria were thought of, all the world knew that 

 iinthrax was infectious from animal to animal, and in some 

 -cases from animal to man. In some Continental districts it 

 has caused terrible destruction of cattle and sheep. In England 

 it is less prevalent, but many workmen woolsorters and workers 

 on skins have fallen victims to it. Twenty years ago its cause 

 was unknown. All sorts of theories were invented to account 

 for its existence. Of course climatic influence, weakness of 

 system, faulty secretions, bad diet, damp pasturage, and all 

 the other thousand and one makeshifts for covering ignorance 

 were made to do duty. At length Davaine, attracted by some 

 experiments of Pasteur, turned his attention to anthrax, 

 ^nd discovered that in the bodies of animals, dead from the 

 disease, there exists rather large forms of bacillus, which 

 appeared to him to be difnerent from the ordinary micro- 

 organisms found in putrefaction. He was not long before 



