ABSTRACTS
351
revealed changes associated with poliomyelitis. A detailed account of investigations
into various aspects of the disease and transmission experiments is given. Attempts
to reproduce the disease in sheep by intracerebral inoculations with filtered brain sus-
pension gave negative results. But unfiltered material or cultures inoculated intracere-
brally, subcutaneously or intramuscularly into sheep and pigs produced lesions identical
with those seen in natural cases. Intranasal instillation of the virulent material failed
to transmit the disease.
Direct cultures from the brain often remained sterile but in order to isolate the
organisms large quantity of brain suspension had to be planted on agar or liver infusion
agar. The organisms remained viable in brain tissue for several months when stored
in 50 per cent neutral glycerine in the refrigerator.
The authors state (details not recorded) that Listerella (ovis) can more consistently
be isolated from brain of rabbits inoculated intracerebrally with infected tissue.
[J.A.I.]
' Swayback', a demyelinating disease of lambs with affinities to Schilder's
encephalitis in man. J. R. M. INNES and G. D. SHEARER (1940).
J. Comp. Path. 53, 1-44
B ESIDES the well-known group of neurotropic virus infections, in which there
is a greater tendency for the disease to affect the gray matter (polioclastic types
of encephalitis), there are several affections of the central nervous system which may
be grouped as the demyelination diseases (myelinoclastic types of encephalitis),
in which the essential lesion, in contrast with the former group, is demyelination.
This demyelination may occur as scattered foci (in disseminated sclerosis), as perivascular
areas (in post-vaccinial encephalitis), or as massive, diffuse, sometimes symmetrical
areas (in Schilder's disease — encephalitis peri-axialis diffusa). So far, all attempts
to establish the aetiology of the demyelination diseases have failed, and it has not been
possible to substantiate any of the aetiological factors that have been periodically;
suggested, such as, toxins, viruses, lead poisoning, anaphylaxis, etc. Experimentally-
demyelination is reported to have been produced by tetanus toxin, CO poisoning,
saponin, etc.
Examples of the myelinoclastic types of encephalitis are also known among animals,
such as, ' post-distemper ' and ' anti-rabic ' encephalitis in dogs and a disease of
monkeys resembling Schilder's encephalitis. Preliminary studies on ' swayback '
had shown that this affection represented the nearest analogy in animal pathology to.
the more idiopathic demyelination diseases of man.
' Swayback ', also known to British shepherds by other names, all apparently
derived from the outstanding symptom of incoordination, is a progressive, non-febrile
disease of newborn and young lambs with a wide distribution in England. Reports of
similar affections are available from Peru, Sweden, Australia, New Zealand and India..
Affected cases show a definite ataxia marked by a varying degree of spastic paralysis.
of the limbs, with partial or total inability to stand or walk, a straddled, staggering
gait, and in occasional severe cases blindness. The disease is generally fatal and death
occurs in a few days to a few weeks from broncho-pneumonia, other secondary infections
like pleurisy and purulent meningitis, or simply marasmus.
The incidence in Britain varies annually and may be as high as 90 per cent of the
lambs born on any one affected farm.
In some areas the disease was seen to be en-
zootic.
Gross pathological changes were present in 101 out of 167 carcases autopsied.
These were confined to the central nervous system, the essential lesion being a diffuse,
symmetrical destruction of the cerebral white matter which was replaced by a loosely
woven, grayish, gelatinous substance or was completely liquefied resulting in the forma-
tion of cavities. A ' retraction ' or ' atrophy ' of the brain was noticed, accompanied
by considerable increase in the cerebrospinal fluid and, particularly in severe cases,
slight to moderate hydrocephalus of the lateral ventricles.