LUNG PLAGUE BY MEDIATE CONTAGION. 
25 
Gadsden will at once admit that the susceptible animal need not 
come into actual contact with the diseased tissues in order to be 
infected. It is the products of the diseased lungs, coughed out or 
breathed out, that become the medium through which the infec¬ 
tion is conveyed. Here then incontestibly the virus is conveyed 
through a medium—the infected mucus , or the infected air. The 
case then is not one of actual contact with the living diseased 
animal. 
Take another case. In our large distillery stables the cattle 
are fixed in separate stalls or boxes, from which, as a rule, there 
is no exit until they leave to go to the butcher. In these, there¬ 
fore, according to the doctrine of the necessity of actual contact 
with the living animal , the disease could only progress along a 
single line of stalls, and would bo impotent to extend across the 
narrow passageway to the next. But who ever heard of lung- 
plague confining itself to a single line of stalls in a distillery stable, 
or to two adjacent lines of stalls in which the animals faced each 
other? More than this, if an insusceptible animal was sandwiched 
in between two susceptible ones, it ought, according to the actual 
contact theory, to prove an insuparable barrier to the further prop¬ 
agation of the disease along that line of boxes, because actual 
contact could not take place across the intervening boxes occupied 
by the insusceptible animal. But we all know that the interven¬ 
tion of one or two such insusceptible subjects proves no barrier 
to the propagation of the disease along a given line of stalls. 
Here there can be no actual contact , hence the resulting infec¬ 
tion is through, the atmosphere or some other medium. 
Another common occurrence in the distillery stable is no less 
conclusive. There is a tendency to a more rapid propagation 
of the infection along a given line, but it is always in a definite 
direction, determined by physical conditions. The troughs into 
which the swill is run are gently inclined from one end to the 
other of a line of forty or fifty cattle, and the swill is run into 
the higher and flows slowly along to the lower one. The rapidity 
of the propagation of the disease depends a good deal on the end 
of the trough at which the first diseased animal happens to stand. 
If at the elevated end, the propagation of disease along the row 
of cattle is rapid, but if at the depressed end, the propagation of 
