REMARKS ON MICRO-ORGANISMS. 853 
although the broth has lost only a very small proportion of 
its substance by weight, and although, as aforesaid, it has not 
undergone putrefaction, and still constitutes an excellent 
pabulum for ordinary forms of bacteria, the bacterium of the 
fowl-cholera, though introduced from some new source, is 
incapable of growing in it. This fact certainly seems highly 
suggestive of an analogy with the effects of vaccination, or 
those of an attack of measles or scarlatina in securing immunity 
from the disease for the future. Here we have a certain 
medium invaded by a virus capable of self-multiplication, as is 
the case with those diseases in the animal body; the medium 
itself little affected chemically by the growth of the virus 
within it, nevertheless rendered unfit for the development of 
that virus for the future. But something more than the 
suggestion of analogy with vaccination has been effected by 
M. Pasteur. By cultivating this bacterium in a particular 
manner, which he has not yet published, he enfeebles the 
organism, as he believes, and produces such an alteration in 
it that, when inoculated into a healthy fowl, it produces only 
a modified and no longer fatal form of complaint, but the 
bird is thereby rendered secure against taking the ordinary 
form of the disease. It has been really vaccinated, if we adopt 
M. Pasteur’s extension of the term vaccination to other 
similar cases; for just as we speak of an iron milestone, we 
may, if we please, apply the term vaccination to the use of a 
virus other than the vaccine obtained from a heifer. But 
though the vaccination with the modified bacteria and the 
fowd-cholera does not occasion the fatal disease, it produces 
pretty severe local effects. If inoculated on the breast of the 
fowl it causes a limited gangrene of the pectoral muscle, the 
affected part falling off in due time as a dry slough. Through 
the great kindness of M. Pasteur, I have now the opportunity 
of showing to the Section a hen which has been treated in 
this way. You observe a slough on the breast of the bird, 
about as large as a penny piece; it is dry, and obviously old. 
The fowl has been some days in my possession subsequently 
to its journey from Paris; but though more than enough time 
has elapsed since the inoculation to have caused its death, 
had the disease been in the ordinary form, it is, you see, in 
good health, bright and active, and it both eats and sleeps 
well.* 
I will now return to the Bacillus anthracis, with regard to 
which I shall have again to refer to the labours of M. Toussaint. 
First, how r ever, I must allude to the work of some of my own 
* M. Pasteur’s researches on this subject are related in the Comptes 
fiendus de VAcademic de Science , February, April, and May, 1880. 
