INOCULATION WITH DILUTED VIRUS. 
69 
with diluted virus, though, as the remaining experiments have 
only recently been communicated to the Department of Agricul¬ 
ture, it would be premature for me to publish details at present. 
1 may say, however, that with dilutions beyond 1 to 100,000, I 
have had no results, and it appears that inoculations with dilu¬ 
tions of 1 to 80,000 would give the local lesion and immunity to 
the most susceptible birds, and that the remainder could then 
be safely inoculated with a dilution of 1 to 10,000, which would 
grant immunity to all or nearly all. The experiments are still 
too few, however, to enable us to be perfectly certain in regard to 
the strength of virus to use with the greatest safety. The birds 
protected in this way have not only been tested with strong virus, 
but they have been placed in infected runs with sick birds, and 
in no case has there been a failure to resist the contagion. 
From these experiments a number of exceedingly important 
conclusions may be safely drawn : 
First .—A single disease-germ cannot produce this extremely 
virulent disease; it cannot even multiply sufficiently to produce 
the local irritation at the point of inoculation. When a quantity 
of virus was introduced into the tissues, which should have con¬ 
tained at least twelve germs, there was no effect, either general or 
local, but by increasing this one-third with the same birds, the 
local irritation appeared. 
Second .—It is apparent that the local resistance to the germ 
fails while the constitutional resistance may still be perfect, and 
that in this case there may be a local multiplication of the organ¬ 
isms for two or three weeks without any disturbance of the gen¬ 
eral health. 
Third .—That this local multiplication of the virus is suffi¬ 
cient to grant a very complete immunity from the effects of such 
virus in the future. 
From these conclusions it follows that the most virulent virus 
may be diluted to such an extent as to become practically a vac¬ 
cine, and that in this condition it may be used safely for produc¬ 
ing insusceptibility. 
These facts are not exactly what we should have expected 
from theoretical considerations, but unless I am greatly mistaken, 
