438 
Journal of Agricultural Research 
Vol. XXX, No. 5 
Washington, D. C.; dog to rabbit to 
dog 630. Dog 630, the animal used, 
was inoculated intraocularlv on Octo¬ 
ber 24, 1923. On November 12, 1923, 
the animal presented clinical sumptoms 
of rabies. 
Each dog in the experiment was 
placed in the same cage with dog 630. 
In each instance the animals were 
attacked and bitten by the rabid dog. 
Each animal was left in the cage until 
it was definitely seen that wounds were 
inflicted. The effort was made to give 
all the dogs the same degree of expo¬ 
sure. The results of the test are given 
in Table V. 
Against a still different strain of 
street virus (B. A. I. 474), however, 
practically no protection was afforded 
to vaccinated animals exposed by intra¬ 
ocular injection. Of 30 vaccinated dogs 
exposed to this virus, 6 survived. 
A study of the vaccines indicates that 
the source, age, etc., had no bearing on 
the outcome of the various experiments. 
All the vaccines used in these experi¬ 
ments were prepared from the same 
strain of fixed virus, which had its origin 
in the Pasteur Institute of Paris, 
France. The results of the experi¬ 
ments herein reported indicate that this 
strain of fixed virus, when used as a 
Table V .—Data of experiment No. 5 
Dog 
No. 
Vaccine * 
; Amount 
j injected 
1 
Date vaccine 
was injected 
Date exposed 
to virus b 
Result c 
56 
B..... 
| 
C.c. 
5 
Nov. 28,1922 
Dec. 13,1922 
Nov. 28,1922 
Nov. 12,1923 
do 
Alive Apr. 12, 1924. 
Do. 
Do. 
57 
B.... 
5 
58 
B. A. I. 
5 
_do. 
59 
A_ 
5 
Jan. 13,1922 
do i 
Do. 
Dead Dec. 3, 1923; rabies. 
Alive Apr. 12, 1924. 
Do. 
63 
_do. 
64 
65 
do 
82 
Do. 
83 
_do. 
Dead Dec. 3, 1923; rabies. 
° Vaccines A and B were from two different commercial houses manufacturing this product. Vaccine 
B. A. I. was prepared in the laboratory of the Bureau of Animal Industry. 
b These animals were exposed to the bites of a rabid dog, No. 630. 
* Diagnosis of rabies made clinically and by microscopic examination. 
Experiment No. 5 may be summa¬ 
rized as follows: Four vaccinated dogs 
and five control dogs were exposed to 
the bites of a rabid animal; two of the 
five controls succumbed to rabies. 
None of the vaccinated animals devel¬ 
oped the disease. 
The number of animals exposed to 
rabies and not treated in which infec¬ 
tion developed has been estimated by 
various investigators to be between 16 
and 60 per cent. In this experiment 
40 per cent of the nonvaccinated ani¬ 
mals bitten developed the disease. In 
view of the fact that none of the vacci¬ 
nated animals developed the disease, it 
can be assumed that the vaccine 
afforded protection in this experiment. 
DISCUSSION 
From the foregoing experiments it 
appears that the efficacy of the single 
injection canine rabies vaccine as a 
prophylactic depends on the street 
virus to which the vaccinated animal 
is exposed. Against intraocular injec¬ 
tions of two different strains of street 
virus, distinct protection was afforded 
by the vaccine, 12 out of the 16 vacci¬ 
nated dogs being protected. 
vaccine, protects against certain strains 
of street virus, but that one strain 
of street virus was encountered against 
which no protection could be obtained. 
The question as to whether these 
results are due to a difference in viru¬ 
lence of the virus used and not to a 
distinct difference of strain can be 
answered, it is believed, by a compari¬ 
son of experiments Nos. 2 and 4. 
In experiment No. 2, using the strain 
of virus B. A. I. 474, the three control 
dogs died of rabies in 15, 29, and 49 
days. Assuming the incubation period 
of the disease to be an index to the 
virulence of the virus, it would appear 
that this virus was not extremely viru¬ 
lent. 
In experiment No. 4, 1 of the 6 con¬ 
trol dogs showed symptoms of rabies 
on the sixteenth day, 4 on the seven¬ 
teenth day, and 1 on the twentieth day. 
This incubation period would indicate a 
higher degree of virulence for this virus 
than for B. A. I. 474, yet 7 out of 10 
dogs were protected against this virus, 
while 5 out of 6 dogs exposed to B. A. I. 
474 virus died of rabies. These facts 
point to the possibility of the existence 
in this country of more than one strain 
of street virus. 
