396 ON THE RELATIONS OF MICRO-ORGANISMS TO DISEASE 
induced to form spores there, the modified organism might yet grow in the 
blood of a living animal. The carrying out of this idea was crowned with 
success ; and, by injecting various different quantities of the liquid containing 
the organism into different individuals, Buchner at length succeeded, both in the 
mouse and in the rabbit, in developing true Bacillus anthracis out of the progeny 
of the hay-bacillus. When large quantities were introduced, the animals died 
rapidly from the merely chemical toxic effects of the injected liquid; but in 
some instances in which a smaller amount was injected, after the period for 
these primary effects had passed, a fatal disease supervened—attended, as in 
anthrax, with great swelling of the spleen, the blood of which was found peopled, 
as in that affection, with newly formed bacilli; and the spleens affected in this 
way were found to communicate anthrax to healthy animals, just like those of 
animals which have died of ordinary splenic fever.* 
Supposing these results to be trustworthy (and the record of them bears 
the stamp of authenticity), I need scarcely point out to a meeting like the present 
their transcendent importance as bearing upon the origin of infective diseases, 
and their modifications as exhibited in epidemics. 
I trust that these examples may suffice to convey some idea of the work 
now going on with reference to the relations of micro-organisms to disease. 
Since the above address was delivered, M. Pasteur has published the method 
by which he produces the ‘attenuation’ of the virus, or, in other words, the 
enfeeblement of the organism of fowl-cholera which fits it for securing immunity 
from the fatal form of the disease. This method consists in cultivating the 
organism, pure and unmixed, in chicken broth, to which access of air is permitted 
while dust is excluded, and simply allowing some months to elapse before it is 
employed. If the period does not amount to more than about two months, 
the organism retains its virulence little abated, but if the period is extended 
to three or four months it is found that animals inoculated with the organism 
take the disease, but have it in a milder form, and a considerable proportion 
recover ; and if the time is made still greater, as, for example, eight months, 
the organism has so far lost its potency that though chickens inoculated with 
it still go through an attack of the disease, allrecover. If the period is sufficiently 
prolonged, there comes a time when the organism is found to have lost its vitality 
altogether, so that it will no longer give rise to new development when intro- 
duced into fresh cultivating liquid. 
In considering by what agency this enfeeblement of the organism and 
ultimate extinction of its vitality was brought about under the circumstances 
* See Ueber die experimentelle Erzeugung des Milzbrandcontagiums aus den Heupilzen, von Hans 
Buchner, Munchen, 1880. 
