EPIZOOTIC APHTHA. 353 
by one or other or all of the sccreting surfaces. Hence, like other 
zymotic diseases, this is altogether specific in its cause, its nature, and 
its mode of propagation. As known in Western Europe and America, 
this disease is invariably due to a virus or contagion thrown off by some 
animal suffering from the disease; itis always manifested by a slight 
preliminary fever, and a period of eruption and decline, and these are 
respectively of constant and well-defined duration. These different 
periods of the disease are characterized by varied manifestations. The 
first period is that of incubation, during which the poison germs are in 
the body of the animal, and propagating themselves there, but have 
not yet affected the constitution so as to impair the functions, or give 
rise to the more manifest symptoms of illness. Toward the end of this 
period, however, the thermometer shows an increase of temperature, in 
the interior of the body, of about two degrees beyond the natural 
standard. ‘This period lasts twenty-four to forty-eight hours, though in 
rare cases it may apparently extend to a week. 
itis followed by the period of eruption, which is first manifested by the 
redness, heat, and tenderness of the udder and teats, of the space 
between the hoofs, and of the membrane of the mouth. In the course 
of one day more, these parts are found to be the seat of numerous hem- 
ispherical elevations or blisters, caused by the effusion of a clear yel- 
lowish fluid from the blood-vessels beneath the cuticle or scarfskin. 
These increase in size for the next two or three days, burst, and dry up. 
The period of decline is marked by the drying and scabbing over of 
the sores caused by the rupture of the blisters, and by the reproduction 
of the lost cuticular covering or scarfskin. The elevated temperature, 
which had declined somewhat on the appearance of the blisters, now 
entirely subsides, unless maintained by exposure, or the irritation of 
the sores by dirt or other bodies. This period has passed and the 
disease is at an end by the fifteenth day, in favorable cases. 
CAUSES. 
The only known cause of itself capable of inducing the disease is 
contagion, or contact of a sound animal with the virus discharged from 
the sores of an aphthous patient. Many accessory causes may be named, 
such as a wet; muddy season, which insures the contact of the virus 
deposited on the soil with the skin about the top of the hoofs; the accu- 
mulation of cattle in large fairs or markets; the aggregation of large 
numbers of live stock for the supply of armies in the field; travel of 
stock by rail or road, and the lfke. Yet these are but means of the 
diffusion of the poison, while no one of them, nor all taken together, 
can call the disease into existence where the poison is not-already 
present. Though prevalent extensively in Europe during or after almost 
every great war since 1695, it did not reach Great Britain till 1839, when 
it was brought by some Dutch cattle imported into London. In the same 
year it was brought by Dutch cattle to Cork, Ireland; and, as free trade 
in continental cattie was established four years after, it has been since 
steadily maintained by the constant importations. In 1841 it is first 
reported in Denmark, a country which breeds its own stock, and rarely 
imports any. Last year appears to have been the first time it appeared 
on American soil, and it has not yet reached the great stock ranges of 
Australia. In Great Britain it spreads widely every year, after the 
great autumn markets, in which home and foreign store cattle mix freely, 
and yet there are in that country many breeding districts into which 
Strange stock are never taken, and where the disease has not yet pen- 
23 A 
