THE RELATIONS OF MICRO-ORGANISMS TO DISEASE, 335 
the bacterium has grown for a certain time in a given por- 
tion of chicken broth, it ceases to develop further ; and when 
this is the case, 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 intro- 
duced from some new source, is incapable of growing in it. 
This fact 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 dis- 
eases in the animal body; the medium itself little affected 
chemically by the growth of the virus within it, but never- 
theless 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 of the fowl- 
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 inocu- 
lation to have caused its death, had the dieease been in the 
ordinary form, it is, you see, in good health, bright and 
active, and it both eats and sleeps well.! 
' M. Pasteur’s researches on this subject are related in the ‘Comptes 
Reudus de l’ Académie des Sciences,’ February, April, and May, 1880. 
