340 
D. E. SALMON. 
who cultivate in but a drop or two of fluid in a small cell—but it 
is our object to give a scientific demonstration, and not to follow 
in the uncertain footsteps of those who have preceded us. To 
test the extent to which the virus may be diluted, we inoculate 
healthy fowls with a drop of various dilutions of our cultivation- 
liquid, obtained as above, and which may be called the first gen¬ 
eration, and we find that a dilution of 1 to 2000 almost invaria¬ 
bly produces death. The virulence of a first cultivation then 
proves nothing, and we must stop to inquire the extent to which 
virulent liquids may be diluted and still prove fatal when there is 
no opportunity for reproduction. Experiments show that death 
is frequently produced by dilutions of fowl cholera virus of 
10,000, but rarely by those of 1 to 20,000 or 1 to 40,000, and 
seldom, if ever, by greater dilutions. 
We are now in a position to judge if the virus really multi¬ 
plies as we know the bacteria do. We have found the extent to 
which the first generation must be diluted to destroy its virulence 
and we make a second cultivation which dilutes the first as the 
first dilutes the blood ; after twenty-four hours we start a third ^ 
cultivation, and now the first is diluted in the proportion of 1 to 
4,000,000, or far beyond the extent to which it was found possi¬ 
ble to dilute it without destroying its properties when no cultiva¬ 
tion was allowed. Have we in this case destroyed the virulence ? 
No, indeed; a single drop of the third, fourth, fifth or sixth culti¬ 
vation will destroy ten thousand fowls as surely as a drop of the 
first. The virus has been cultivated then, has multiplied, and is 
capable of indefinite multiplication. Our liquid swarms with mi¬ 
crococci, and nothing else can be found by the most careful mi¬ 
croscopic examination. If we expose virulent liquids to atmos¬ 
pheric germs, putrefaction soon occurs, and their activity is lost. 
Why has not the same result followed in our cultivation-liquids, 
if the bacteria multiplying in them were foreign to the virus ? 
Have we not, even here, a strong indication that these organisms 
are the active principles of the virus—that they produce the dis¬ 
ease ? 
3. The living bacteria are required, to produce the malady. 
There are three hypotheses which one must take into account in 
