72 
JD. E. SALMON. 
In the report of the Bureau of Animal Industry for 1885 (pp. 
121 and 122), I have collected a number of cases where outbreaks 
of pleuro-pneumonia were started in uninfected herds by the 
practice of inoculation. These certainly are cases of mediate 
contagion. 
But why stop to quote cases ? They are innumerable. There 
is scarcely a man who has had a large experience with pleuro¬ 
pneumonia but that has seen equally satisfactory cases, and many 
others which indicated if they did not prove the dissemination of 
the plague by mediate contagion. 
So much for the facts. Let us turn for a moment to the the¬ 
ory and inquire how this doctrine of contagion by contact with 
the living diseased animal only can be explained. How does 
the living diseased animal communicate the contagion ? Evi¬ 
dently by means of the expired air. This expired air, then, must 
be charged with the germs of the disease, and it becomes so 
charged by coming in contact with the infectious matter formed 
in the lungs. Suppose this air is expired into a close, badly ven¬ 
tilated stable, the whole air in that stable becomes charged, does 
it not? We know from experience that in such a case the con¬ 
tagion may skip a dozen or twenty cows to infect the farthest 
one in the row. This demonstrates that the contagion is held in 
the air for an appreciable time and may be carried some distance 
in such a building and still be able to infect. How long is it 
held in the atmosphere? One minute, or ten minutes, or an 
hour ? Who can answer ? Will any one say it cannot be thus sus¬ 
pended one minute or ten minutes without losing its infective 
properties ? And vet the advocates of this strange theory will 
tell you that if the sick cow is taken out of such a stable, and a 
susceptible healthy animal introduced only a second afterwards, 
the fresh cow is perfectly safe! The disease can only be con¬ 
tracted from contact with the living diseased animal. 
They will also tell you that although the air expired by the 
living diseased animal contains the germs of contagion, you may 
take the warm and steaming lungs from a freshly killed animal 
and allow other cattle to breathe the exhalations, and the residual 
