CATTLE, THEIR DISEASES, 
263 
may be carried by the many. That it may be taken in pastures and with 
fodder is too well authenticated to leave room for doubt. 
Vitality of the Virus, 
There is much difference of opinion with regard to the power of tho 
Tirus to resist ordinary destructive influences. In many cases the free 
jexposure of an infected place for three or four months to the action of 
the air has purified it so that fresh stock have been introduced with 
impunity. On the other hand, instances can be adduced in which cattle 
have been infected by being placed in stables in which cattle had not 
been kept at least four months previously. Other things being equal, it 
will be preserved longest where it has been dried up and covered from 
the free access of the air. Thus in very dry and close buildings, in those 
having rotten wood-work, or deep dust-filled cracks in the masonry, anl. 
in those with a closed spaoo beneath a wooden floor, it clings with tho 
greatest tenacity. Again, when the buildings contain piles of lumber, 
litter, hay, fodder, or clothing, the virus is covered up, secreted and 
preserved for a much longer time than if left quite empty. In these 
last it is preserved just as it is in woolen or other textile fabrics, and 
carried from place to place by human beings. 
As carried through the air, the distance at which the virus retains its 
.infecting properties varies much with varying conditions. The author 
has seen a sick herd separated from a healthy one by not more than 
fifteen yards and a moderately close board fence of seven feet high, and 
in the absence of all inter-communication of attendants, the exposed 
herd kept perfectly sound for six months in succession. On the other 
hand, infection will sometimes take place at a much greater distance 
‘without any known means of conveyance on solid objects. Roll quotes 
150 to 100 feet, while others claim to have seen infection at a distance of 
200 and 300 feet. But it may well be questioned whether in such cases 
the virus had not been dried up on light objects, like feathers, paper, 
straw, or hay, which could be borne on the wind. This, from being in 
thicker layers, would escape the destruction that would have befallen it 
had it been carried in the air only as invisible particles'. 
i How the Infection Enters the System. 
The seat of the disease, its progress, and tho result of all attempts at 
inoculation, favor the presumption that tho virus is usually taken in with 
the air breathed. Not only are the lesions concentrated in the lungs, 
but they begin with cloudiness and swelling of the smaller air-tubes and 
surrounding connective tissues* 
