J. F. SHIRLAW                                         353

that equine encephalomyelitis is caused by the ingestion of toxic forage and
this idea of fodder poisoning is one that is still held in many quarters. This
theory may be briefly disposed of by stating that:—
         (a) Examination of the stomach ingesta of all horses succumbing
                to the disease was negative for group alkaloid test.
        (b) A series of rabbits and guinea-pigs fed on these samples ad lib.
                remained free from any symptom, toxic or otherwise.
        (c) The withholding of suspected forage and its replacement by fresh
                supplies did not result in any cessation of the disease.
         (d) Samples of forage appeared perfectly sound and were free from
                mouldy decomposition and poisonous seeds, (e.g. Abrus pre-
                catorius). The feed was carefully balanced and there was no
                probability of a cereal (phytic acid) poisoning.
        (e) The grasses and grains fed to horses during the Multan outbreak
                were examined by competent agricultural botanists who could
                detect no potentially poisonous species.
        (f) The same forage from exactly the same source of supply, was
                fed to other cavalry regiments, which remained entirely free
                from disease.
         (g) There is no proof that forage poisoning, whatever that term may
                mean, can be responsible for pathological lesions in the central
                nervous system of the type described.

The toxic etiology of the disease was one seriously considered by the
writer and finally abandoned in favour of a virus theory, in view of the fact
that the disease on epizootological and pathological grounds was strictly
comparable with a variety of forms of equine ancephalomyelitis, in many of
which the existence of a virus has been proved.

The earliest experiments were performed on horses, aged army casters
being the only animals available, and in rabbits and guinea-pigs. The results
of a successful subdural transmission in horses has been recorded [ Mosley,
Hean and Shirlaw, 1934]. The clinical syndrome of these two cases was
typical of the affection. On post-mortem examination, specific lesions of
equine encephalomyelitis were found in the central nervous system and the
kidney. Mention has also been made of the failure to reproduce the disease
in horses by intrathecal inoculation of brain emulsion. This failure was
anticipated. The resistance to passage of virus particles on part of the
meningo-encephalic barrier is well known.

The first series of rabbits and guinea-pigs was inoculated as follows :—
Small portions of brain were removed immediately after destruction of
hopeless cases (Multan outbreak) and rushed to the laboratory at Lahore
in thermos flasks packed with ice. The tisssue invariably arrived in a frozen
state and small pieces of representative areas of the brain were quickly
triturated in saline and sterile sand. After being allowed to settle in the
refrigerator for eight hours, the supernatant fluid was aspirated. This con-
stituted the inoculum. Rabbits and guinea-pigs, two for each specimen,
were trephined and subdurally inoculated with 0.1 c.c. of the inoculum, the
procedure being the same as for the propagation of rabies virus in the
manufacture of Semple's vaccine.