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What may be the nature of these cell inclusions in the cat is an open question. There is no
reason to suspect that they are parasitic if they are commonly found in normal cats both in
Europe and Asia, but not in anyother animal. More probably they are some vestige of another
structure such as the bodies known in cytological nomenclature as a plastids". It would, however,
be interesting to learn if they can be found in other felidae, say tigers or panthers.
In what does the difference between street virus and fixed virus lie ? If the former can be
changed into the latter with certainty by subdural passages in suitable animals, should. it not be
possible to effect the reverse change and to cause the reappearance of the large and numerous
Negri bodies ? The transformation of the large, easily seen Negri bodies, which are an
accompaniment of the disease when its incubation period is long and irregular, into the tiny and.
difficult to recognise bodies, which are alone as a rule to be found when the disease has its
incubation period reduced to a minimum and quite regular, is secured by subdural passages
through susceptible animals. Pasteur found that 50 passages or so were required in the case of
rabbits Other workers have obtained a virus, fixed as regards its incubation period, by fewer
passages, e.g., six, when smaller animals such as guinea pigs or rats were used, but, with the
exception of Schiffmann (19) wh.o treats of rabbits, no one has recorded simultaneous observations
of the alterations in the form of the Negri bodies which occur daring the progress of such
series. (vide p. 15). Acting on the supposition that the large Negri bodies may only be developed
when there is some resistance to infection, as is unquestionably the case when the subcutaneous
route is chosen or when naturally resistant animals are subdurally injected, we made an attempt
with rats, but failed. We next tried with guinea pigs, but in them subcutaneous inoculations
failed after three or four passages, and in the brains of the ones that died none of the larger
Negri forms were seen.
'Birds, as is well known, are remarkably resistant to rabies and. it appearst hat even when
successful subdural inoculations are made the virus dies out after a very few passages.
TABLE No. 11 showing the result of fixed virus subdural inoculations in hens.
,
Virus inoculated. Incubation period Microscopic findings.
Serres
No. 1.
Hen 1
Fixed Virus Rabbit 14 days ,.. Negri bodies 1µ — 4 µ numerous.
(1) brain subdurally.i
Hen 3
... Brain Hen I sub-
durally.
28 days ... Negri bodies 10µ cerebellum.
2µ cortex.
Hen 5
... Brain Hen 3 sub-
durally.
16 days ... Negri bodies 4µ cortex.
Hen 6
... Brain Hen 5 sub-
durally.
Survived.
Guinea pig 1 Brain Hen 1 sub-
d.urally.
7 clays ... Negri bodies in hippocampus major and cortex, tiny but numerous.
Guinea pig 3 Brain Hen 3 sub-
durally.
22 days ... Negri bodies in hippocampus major and cortex, tiny, fairly numer-
ons ; blue dots.
Guinea pig 5 Brain Hen 5 sub-
6 days ...
durally.
Negri bodies to 5µ in cerebellum, tiny in cortex.
Series No. 2.
Hen 2
... Fixed Virus Rabbit 14 clays ... Negri bodies 1µ—4µ numerous.
(2) brain subdurally.
Hen 4.
Brain Hen 2 , sub-
durally.
Survived.
Guinea pig 2 Brain Hen 2 sub-
durally.
11 days ... Negri bodies tiny but numerous, blue dots.
Hen 1 was inoculated. subdurally with fixed virus from a rabbit whose hippocampus
showed no Negri bodies. Incubation 14 days, death four days later. Numerous small Negri
bodies, the largest not more than 2 µ in diameter, were readily seen in the cells in various parts
of its brain, none in the retina.
A guinea pig inoculated subdurally from the brain of Hen 1 had an incubation of 7 days.
In its hippocampus Negri bodies were numerous but tiny. They were, however. much more
easily recognised than would have been the case if the virus had not passed through the bird. In
•
Note.—Since this was written we have been able to examine the brain of a normal panther kindly sent by
Dr. Sheldon. Similar bodies 1 . 5 µ in size were found in the hippocampal cells.
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