20
perfect morula. Though at first glance deceptive there was never any real doubt that the forms
we saw were not Negri bodies.
Returning to the presence of Negri bodies in the retina, which we brought forward in section
2 as a useful aid to diagnosis in doubtful cases, it may be worth. while to describe the methods
followed. In the first place the eye should be extracted as soon after death as possible, for the
retinal elements quickly undergo destructive changes, though these are less noticeable in the cells
of the ganglionic layer with which we are particularly concerned than in the more delicaté rods
and cones. The eye may be fixed as a whole in acetic bichromate mixture or the retina may first
be dissected out and fixed alone. We found the latter a tiresome procedure and usually fixed the
whole eye. After fixation the retina must be dissected out and may either be made into a ball with
collodion or lifted about as it is and embedded in paraffin in the usual way. The section should
not be more than 4µ— 5µ in thickness.
The best stain is Mann's mixture. To get certain results the eye must be fresh, the sections
of the best and the staining perfect. The whole process is scarcely more laborious and difficult
than getting a good preparation of any part of the brain. Negri bodies appear as brightly stained
reddish dots in the pink cytoplasm of the cells of the ganglionic layer, often with an unstained
area round them. They are seldom as much as 2µ in diameter and generally less. Not every cell
contains the bodies, perhaps only 1 in 10 of those cells which are sufficiently well displayed to the
view, but then. it must be remembered that the cells are only seen in thin section. As many as
ten have been seen in one cell, but usually there are not more than one or two. Their distribution
is irregular, but it does not seem that they are confined to, or are more numerous in, any particular
region of the retina.
Even when no Negri bodies can be seen there is often considerable degeneration of the
ganglion cells; the nucleus becomes indistinct or disappears, the cytoplasm vacuolated and the
chromatic substance collects at the periphery of the cell. Occasionally 1 to 5 tiny, deeply stained
blue dots, scarcely 2µ across, have been noticed in cells which do not contain Negri bodies, but
their significance is unknown.
The condition of the spinal ganglia in street virus deserves especial mention. By no means
all the cells contain Negri bodies. In the same field it is possible to find cells apparently perfectly
healthy, others containing one or two Negri bodies, seldom more than 5µ in diameter, and sur-
rounded usually by an unstained area; another cell will be disorganised without showing bodies,
another is invaded and partly replaced. by small round cells and yet another will be packed with
small Negri bodies. As many as 100 have been counted in one cell. When present in such large
numbers the individuals are generally rather indistinctly stained.
The cells lying nearest the outside of the ganglion are the ones which most frequently
contain the greatest number of bodies, and the bodies themselves seem to collect at the periphery
of the cells by preference, though the nucleus sometimes seems to be replaced by a. mass of them.
Both Luzzani (29) and Babes (30) have remarked on the presence in the brains of normal cats
of bodies which might be mistaken for Negri bodies, and. enter a caution as to the diagnosis of
rabies from the microscopical findings in suspected cats. We have examined the brains of two
adult cats and of one kitten about two weeks old. In the latter nothing was found, but in the
two former bodies of a kind were seen with Mann's and Unna's stains.
Cat 1—Hippocampus major. —Scattered in the cells were small round bodies less than 2µ in
diameter, sometimes mere dots. They were not found in the majority of cells, though sometimes
two or three were seen in one cell. They were usually at a considerable distance from the cell
nucleus. A few oval and pear shaped. forms were seen. The outlines of the bodies stained more
-deeply than the centres. No cell degeneration was observed.
In the cortex there were a few tiny forms, in the retina nothing.
Cat 2 —Hippocampus major.—Three tiny bodies were seen in the cell processes, no cell
degeneration.
Cortex.—In the large oval cells, not the pyramidal, some tiny, round or oval, faintly stained
red dots occurring in clumps were seen. No cell degeneration.
It would certainly be possible for any one who had not a fairly extensive acquaintance with.
Negri bodies to mistake these inclusions for them, particularly if only a sample of cortex were
available, but their comparative scarcity, their appearance, the absence of leucocytic exudations
and cell degeneration should. be enough to enable an experienced observer to decide which of the
two he is looking at. This at any rate is the opinion to which our limited observations on only
two oats inclines us. Further practice may cause it to be modified.