THE VETERINARIAN, MARCH 1, 1873. 
Ne quid falsi dicere audeat, ne quid veri non audeat.—C icero, 
THE ORIGIN OE CONTAGIOUS DISEASES. 
Spontaneous origin of anything may always he assumed, 
and cannot easily be disproved. When a number of animal¬ 
cules are formed in a fluid which did not shortly before con¬ 
tain them, it saves a world of inquiry if it can at once he 
allowed that they were developed out of the lifeless constitu¬ 
ents of the material in which they now exist. So, if pleuro¬ 
pneumonia or foot-and-mouth diseases appears in a herd of 
cattle which have not been exposed to direct contact with 
diseased animals, the difficulty of explaining the manner of 
communication is directly removed when the theory of spon¬ 
taneous origin is accepted. 
Infection is a fact which the public mind is not slow to 
realise; but the presence of an infecting germ in the begin¬ 
ning is a fact which people generally are not inclined to 
receive. There is no objection to admit that a disease once 
generated in an animal’s system may spread by infection, 
but when the evidence of communication is incomplete, it is 
convenient to refer the origin of the disease to circumstances 
which affect the animal’s health or comfort. 
Foot-and-mouth disease is a good instance to the point in 
question. The affection arises in places remote from the great 
lines of cattle traffic. No association of healthy with diseased 
animals can be traced, or even reasonably alleged ; but hard¬ 
ships have been suffered, long journeys have been taken, the 
beasts have been shut up in the badly ventilated holds of 
vessels; and what more can he required to cause fever, with 
a few blisters on the tongue, and sore feet ? 
Very few persons talk in this way about cattle plague, 
because that disease is clearly a stranger to this country. 
When it appears, it has been introduced from Russia or 
14 
XLVI. 
