66 
D. E. SALMON. 
accepted, and with reason. A negative result is nothing, it is a 
zero, a cypher, and you may add together a hundred or a thou¬ 
sand cyphers and you get what ? Nothing. But when you get 
positive results you have something tangible, and if you can 
repeat them a reasonable number of times it is a demonstration. 
With this question, however, a few gentlemen have built up a 
theory on negatives, they have scrupulously discarded all posi 
tive results and have apparently convinced themselves at last that 
they have in this peculiar way demonstrated their hypothesis and 
that it is no longer a theory but a fact. If they are reposing 
with dreams that the world at large has accepted their conclusion, 
they are destined to a rude awakening, for they stand to the 
other members of the profession in some such proportion as 
the three tailors of Tooley street to the people of England. 
Dr. Gadsden continues: “In Pennsylvania, the State that I 
have the honor to represent, Dr. Francis Bridge has possibly had 
as large an experience in this disease as any person in the United 
States. In frequent conversations and in letters hereto appended, 
he states most unqualifiedly that the disease can only be com¬ 
municated by contact with the living diseased animal.” Very 
well, Dr. Bridge also believes that it is impossible for an animal 
affected with chronic pleuro-pneumonia to disseminate the dis¬ 
ease. Dr. Gadsden, on the other hand, believes such animals to 
be very frequent sources of the plague. Dr. Bridge’s observa¬ 
tions with chronic cases have been equally extensive with his 
observations on the subject of mediate contagion. Why not 
accept his views on the one as well as the other % What a relief 
it would be in the work of stamping out this treacherous malady 
to be able to overlook chronic cases and infected premises with 
impunity! 
The doctor’s case is rested principally, however, upon the so- 
called experiment with the Shufeldt distillery stables in Chicago. 
He says: “ But perhaps the most conclusive test, and the one on 
the largest scale, was made in the city of Chicago, at the sheds of 
the Shufeldt distillery. These sheds had been occupied with 
cattle affected with pleuro-pneumonia, 455 out of 497 being found 
diseased; and the last ones were slaughtered on December 10, 
