ENCEPHALO-MYELITIS IN AN INDIAN CAVALRY REGIMENT       213

of the nasal passage, and the nasal mucous of infected horses is invariably infectious
while a slight catarrh of the upper respiratory tract is usually present.

It appears that, in the horse, there is more than one type of meningo-ence-
phalo-myelitis, the most important and the most specific being " Borna " disease,
which was first noted in Germany many years ago. In recent years, the amount
of literature published on this disease has been extensive and workers on it may
be divided into three schools :—German, French and American, although in other
countries there are copious records of investigation.

The workers in France have described a disease practically identical with
" Borna " disease but differing from it in certain important characters.

In " Borna " disease the important lesions are confined to the central nervous
system. There is a slight hyperaemia of the meninges of the brain and spinal cord,
and an abnormal fulness of the meningeal vessels, while punctate hæmorrhages are
seen throughout the brain substance, more especially in the grey matter. There is
a well defined perivascular infiltration around the vessels of the choroid plexus and
the small capillaries and veins, frequently extending through the grey matter.

Hutyra and Marek state that subependymal hæmorrhages may be present,
along with slight thickening of the ependyma. Exudation in the meninges is not
found, although Hutyra mentions that the choroid plexus may occasionally show
gelatinous swelling. There is, usually, a well marked mononuclear cell infiltration
in the brain substance with a certain amount of neuroglial proliferation. The most
important feature of " Borna" disease is the presence of intranuclear inclusions
known as Joest-Degen ' bodies, and according to German workers, these bodies
are considered as specific of " Borna " disease as negri bodies are of rabies. As in
rabies, they are found most commonly in the hippocampal gyrus. The same
authorities state that degeneration of the cell nucleus, such as neuronophagia, is not
found in " Borna " disease in Germany.

British workers, while confirming the importance of Joest-Degen bodies, claim
that there is a definite destruction of the nucleus of nerve calls in "Borna"
disease.

In spite of numerous attempts of workers, in the past, to prove a bacterial
etiology, it is generally considered, at the present day, that the various streptococci
and diplococci which can be isolated occasionally from the brains of the diseased
horses are of no importance.

It has been definitely proved that "Borna" disease is due to a neurotropic
virus which possesses a close affinity to the viruses of vesicular stomatitis of the
horse, louping-ill of sheep, and epidemic poliomyelitis of the human subject.