98 
REPORT ON THE CATTLE PLAGUE. 
serous effusion, which by its pressure upon the air-cells and 
their rete of capillary vessels, obstructs both the admission of 
air to the cells, and the circulation of the blood through the 
vessels, and thus leads to an imperfect decarbonization of the 
blood, as well to far more important changes in the fluid itself. 
Not only, in many diseases, are serous exudations entirely 
independent of inflammation, but fibrinous ones are equally 
so in the opinion of some of the ablest pathologists of the 
present day. These deposits may result from the vital force 
of the vessels being impaired by some depressive influence 
acting on the nervous system, either generally or locally, as 
well as by some unexplained or ill-understood alteration 
taking place in the composition of the blood, by the existence 
within it of morbific animal or vegetable products. The 
fibrinous depositions in pleuro-pneumonia succeed the 
serous, and are probably due to either an alteration in the 
relative proportion of the component parts of the blood, or 
an interference with its vitality, brought about by the pre- 
sence of the special materies morbi of the disease, and which 
may have entered it in the ordinary manner of infection. 
The abnormal action which commenced in the parenchyma 
of the lungs extends towards their investing membrane, 
when, from the nature of this tissue, as well as from the 
longer existence of the action itself, an augmented fibrinous 
exudation takes place upon their surface. We regard, there- 
fore, the implication of the pleura as a characteristic of an 
advanced stage of the malady, and also of a still further de- 
terioration of the blood. 
Since the appearance of pleuro-pneumonia no other disease 
of a fatal character, and possessing contagious or epizootic 
properties, has shown itself among our cattle; but in 1847 a 
very fatal malady broke out among the sheep. This affection 
was recognised as the smallpox of sheep ; and it was ascer- 
tained in the most conclusive manner that it had been intro- 
duced here by some “ Merinos,” which had been shipped at 
Tonning, on the coast of Denmark, and also by some others 
shipped at about the same time at Hamburgh for the supply 
of the English market, and in whose systems the disease was 
incubated. From the free commingling of these foreign 
sheep with our own breeds in the London Cattle Market, and 
also from the circumstance that many of them w r ere pur- 
chased by farmers as “ stock sheep,” the smallpox was soon 
spread over a great tract of country, proving destructive to 
life in numerous instances to the extent of even 90 per cent. 
This state of things was met by legislative enactments, 
with the view to arrest the progress of the disease, and hap- 
