Mar. 1 , 1925 
Vaccination Against Rabies in Dogs 
435 
the vaccination had no appreciable 
effect on the incubation period of the 
disease. If the period of incubation 
in the control animals can be used 
as an index of the virulence of the 
virus, it appears that the animals 
were not overwhelmed with virus. 
This experiment confirmed the con¬ 
clusions drawn from experiment No. 1, 
namely, that a single injection of 
vaccine failed to produce sufficient 
immunity to protect dogs against an 
intraocular injection of street virus 
B. A. I. 474. 
The results of the two foregoing 
experiments were in contradiction to 
the results obtained by Eichhorn and 
Lyon, who protected 100 per cent of 
their animals against an intraocular 
injection of street virus. 
In comparing experimental data of 
Eichhorn and Lyon with the preceding 
experiments, it was observed that the 
only practical differences between the 
experiments were the nature of the 
exposure virus used and the personal 
factor of technic. Leaving the 
personal factor aside, the only differ¬ 
ence remaining was the use of a 
different exposure virus. It was con¬ 
sidered advisable at this time to 
inquire into the source of the fixed 
virus used by the various commercial 
houses manufacturing the single¬ 
injection canine rabies vaccine. 
As a result of this inquiry it was 
learned with considerable surprise 
that the virus used by all the com¬ 
mercial houses apparently had a 
common origin, the Pasteur Institute 
of Paris, France. The canine vaccines 
manufactured in this country, 
therefore, are prepared with a European 
strain of fixed virus. As a number 
of the commercial houses manufactur¬ 
ing canine rabies vaccine also prepare 
rabies vaccine for human use, it is 
probable that the fixed virus used 
for this product also had the same 
source. 
There was a possibility, it was 
believed, that there might be different 
strains of rabies street virus against 
which, or some of which, protection 
could not be obtained by immuniza¬ 
tion with the strain of fixed virus 
used as a vaccine. To determine 
this point was the object of experi¬ 
ment No. 3. 
EXPERIMENT NO. 3 
Eighteen dogs were given one 
injection of vaccine. They were then 
divided into three groups of six each, 
and to each group were added four 
normal dogs to be used as controls. 
Each group of 10 dogs (6 vaccinated 
and 4 controls) was exposed to an 
intraocular injection of a street virus 
of different origin. 
Virus No. 1 had the following history: 
Pennsylvania dog to man, to rabbit, 
to rabbit, to dog; 0.1 c. c. of a 1:2 
dilution of the brain of the dog was 
used for exposure. 
Virus No. 2 was the B. A. I. 474 
strain, a 1 : 10 dilution of the medulla 
of dog No. 35, dead December 14, 
and in glycerin since that time. 
Virus No. 3 consisted of small pieces 
of rabid brain material of a New York 
dog, cat, and calf. This material, 
however, had been in glycerin for a 
considerable period of time. 
The results of this experiment are 
given in Table III. 
Table III may be summarized as 
follows: In lot No. 1, exposed to virus 
No. 1, one vaccinated dog died of rabies 
and five survived. Of the four control 
dogs, all died of rabies. Sixteen and 
two-thirds per cent of the vaccinated 
dogs died, as against 100 per cent of the 
control dogs, indicating that consider¬ 
able protection was afforded by vacci¬ 
nation against this virus. 
In lot No. 2, exposed to B. A. I. 474 
virus, four vaccinated dogs died of 
rabies and two survived. Of the four 
control dogs, three died of rabies and 
one survived. Sixty-six and two-thirds 
per cent of the vaccinated dogs died, as 
against 75 per cent of the control dogs. 
This confirms the previous experiment 
in which little or no protection was 
afforded by vaccination against this 
virus. 
Attention is called to dog 47 in this 
lot, which showed symptoms of furious 
rabies March 5 and was found dead on 
the morning of March 6. Extracellular 
Negri bodies of average size were found. 
Rabbits inoculated with brain material 
of this dog were completely paralyzed 
on the seventh day. Four passages of 
this virus through rabbits resulted in 
each instance in the development of 
complete paralysis on the seventh day. 
Negri bodies in these rabbits were 
scarce, but of very fair size. These 
results indicate that the virus in the 
brain of dog 47 had the properties of a 
fixed virus. Whether the exposure 
virus became fixed for the rabbit after 
passage through this dog, or whether 
the animal succumbed to fixed-virus 
infection from the vaccine which 
became exalted as a result of the in¬ 
jection of the street virus, are questions 
difficult to answer. 
In lot No. 3, exposed to virus No. 3, 
one vaccinated dog died of rabies after 
an incubation period of almost four 
