ConcLusions.—Pleuro-pneumonia virus has an absolutely specific
effect on the tissues, it chiefly attacks the connective elements, the lesions
which can be demonstrated histologically are characterised by the follow-
ing phenomena :—

(1) The virus multiplies in the lymph vessels after having invaded
them (lungs, muscles, subcutaneous connective tissue, lymph
glands, intestines and mucosae and serosae generally). It
causes an inflammatory process, which presents itself micro-
scopically as lymphangitis serofibrinosa, lymphothrombosis, emigra-
tion of leucocytes, ete.
(2) The process proceeding only along the lymph vessels (per con-
tinuitatem) involves also the lymph spaces of the walls of
blood vessels, a peri- and mesoarterlitis, with formation of
thrombus results. Thick rings of leucocytes with deposits of
fibrine surrounding the blood vessels at a short distance in
circular symmetrical arrangement give quite a characteristic
appearance to the microscopical lesions.
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(3) The blocking of the blood vessels gives rise to ischaemic necrosis
(Cohnheim), in which all stages of necrobiosis, demarcation, and
of incipient regeneration can be demonstrated.
(4) The dead portion can undergo sequestration, a capsule of con-
nective nature being formed by reactive inflammation (lungs,
muscles), or the primary pleuro-pneumonia process comes to
a standstill, and the tissue become transformed into a cicatrice
by opposition of connective tissue (subcutaneous tissue).
(5) The lesions of pleuro-pneumonia having originated by metastasis
present microscopically the image of a corpuscular infiltration
with pronounced serofibrinous exudation, without there being
any localisation of the process within definite portions of the
tissue. It is in the nature of the virus to form metastases,
especially in the joints, the age of the affected animal being
apparently immaterial.
(6) The histological lesions around the vessels differ from those of
chronic productive pneumonias, and can be used with certainty
for diagnosis.
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: DESCRIPTIONS OF PLATES.”
Plate I.
