AGf~ICULTURAL RESEARCH, PUSA.

4,68 PllACTICAL BACTERIOLOGY
RABIES
This disease is communicated to the human subject
by the bite of a rahid dog or other animal, the
infective virus being present in the saliva of the
animal. When a person is bitten by a dog suffering
from rabies, prophylactic treatment by the Pasteur
method or a modifi.cation must he carried out without
delay, and where there is any doubt as to the
condition of the dog, an accurate diagnosis is essential.
The animal should be killed, and if the laboratory is at
some distance, the head is removed and forwarded in
ice. In the laboratory the scalp is reflected, the skull is
opened by means of sterile bone forceps and the brain
removed with aseptic precautions. The hippocampus,
which forms the Hoor of the lateral ventricle, is dissected
out, smears are made by squeezing a portion of'
the tissue between two slides, and pieces are also fixed
for histological examination. In addition, an emulsion
is prepared for animal inoculation. The smears are
fixed in methyl alcohol for five minutes, and stained by
Leishman's or Giemsa's method (vide pp. 168, 170)
or by Mann's stain. For sections, the tissue is fixed in
formalin (vide p. 178) and stained as above.
The diagnosis depends on the finding of the characteristic
Negri bodies in the cytoplasm of the nerve
cells. They consist of round, oval or anglllar bodies,
varying in size from O·5-25fL, staining' pink with
Leishman's, Mann's or Giemsa's staiu. The nature of
these structures is still a matter of ullcertainty, though
their occurrence is a specific feature of ra.bics.
The virus is localised in the nervous tissues and
salivary glands, and is transmitted through the body
by the nerve fibres only. -:rhc incubation period in
man is usually from thirty to sixty days. 'rhe virus
becomes enhanced in virulence after repeated passage
in the rabbit, until it kills regularly ill six to seven
clays, and then becomes the" ii.xed " virus of PasteuI'.
The virus is easily destroyed by heat alld chemicals,
but is resistant to glycerol. Carbolic acid attenuates