194
Contagious Pleuro-Pneumonia of Goats
for all the local and pulmonary phenomena. Capillary thrombosis probably
plays a large part in the necrosis.
The mode of action of the organism in this ' oedematogenesis ' is peculiar.
Capillary dilatation, which is always a marked feature, is undoubtedly a con-
tributory factor, and is almost certainly the result of toxic action on the nerve
endings, but toxic action on the capillary endothelium, increasing its per-
meability, is also indicated.
Bacterial toxins with this property are almost invariably pyretic, and the
diseases associated with them febrile, in contrast with this disease. The type
of bacterial toxin in question also causes severe direct damage to endothe-
lial cells, with consequent rupture of capillaries and the escape of erythrocytes
at any site of inflammation. As already stated, no such phenomenon charac-
terises either the local or pulmonary lesions caused by this organism. Its
toxic action is clearly peculiar, and worth study. One is vaguely reminded
of the action of histamine.
In one severe local reactor weighing 21 kilos, both hind legs were removed
post mortem and weighed. The normal limb registered 1.75 kilos ; the reacting
limb no less than 4.5 kilos, or more than one fifth of the entire body-weight.
The difference in weight of the two limbs, 2.75 kilos, is attributable only to the
oedema. The blood volume of the goat, according to Dukes (1937), is 6.2
per cent of the body-weight, and in this goat would be about 1.3 litres. In
other words a volume of fluid more than twice that of the animal's blood had
been deviated from the tissue fluids, by a process of dehydration into the effect-
ed area—a truly remarkable phenomenon. It may be added that examina-
tions of the blood-cell volume in similar severe reactors has shown a terminal
increase in the cell volume, indicating a final fall in the total blood volume,
particularly in lean goats where the volume of reserve tissue fluid is small.
The virtual failure to effect transmission by experimental contact is quite
inexplicable, particularly in view of the reputed high infectivity of the disease
in the field, and the marked susceptibility to infection by insufflation. The
method of natural spread must be regarded as a problem yet to be solved.
The bovine disease, however, is similarly erratic in its spread by contact.
The indications of these experiments are that vaccination can be most
reliably effected by the inoculation of fresh pneumonic emulsion subcutane-
ously, at sites other than the trunk and for preference in the ear. There is no
indication that the antigenic value of the inoculum is dependant on its virulence
from the lethal aspect, relatively avirulent inocula proving equally effective.
It is, however, to be borne in mind that all inocula used in the experiments
were prepared only from early pulmonary lesions. It is possible that forma-
lised vaccines have practical value, but in the experiments made by us there is
an indication that they would be less reliable.
The superficial resemblance of the organism in stained preparations to the
Rickettsia is noteworthy. It is noteworthy that the only organism hitherto
recognised as classifiable with that of the bovine disease is the cause of another
goat disease—agalactia. It is also noteworthy that a Rickettsia is accepted as
the etiological agent in heartwater, a disease similarly characterised by trans-
udation through a serous surface, and affecting goats, sheep, and bovines.
There can be no doubt that the organism of this pleuropneumonia of goats
is closely related to that of the bovine disease, and Turner's suggestion that a