22 CANINE DISTEMPER 
weakened the animal’s resistance, thereby opens the 
door to the secondary invaders. Observers have stated 
that the B. bronchisepticus can usually be discovered in 
the respiratory passages of most healthy dogs, though 
I think this argument would not preclude the possibility 
of it being the primary invader; for its pathogenic 
power to set up symptoms would be enhanced as soon 
as the animal became debilitated owing to the agency 
of predisposing causes, such as starvation, bad hygiene, 
cold, etc. The case of tuberculosis is analogous, for we 
know that the tubercle bacillus may frequently be found 
inhabiting normally healthy people without producing 
lesions of tuberculosis. 
Ferry’s answer to the assertion that B. bronchisepticus 
is a saprophyte normally inhabiting the respiratory tract 
of healthy dogs, and which can only be regarded as a 
secondary invader, is: a 
“When this same objection has been brought up in 
discussing some of my papers . . . I have always asked 
the critics if they ever found the organism normally 
themselves, or knew of anyone else, and the answer 
has been in the negative. B. bronchisepticus is not a 
normal inhabitant of the respiratory tract of healthy 
dogs, but these dogs are ‘carriers.’ I have autopsied 
between four and five hundred dogs, both healthy and 
diseased, and speak from experience. I have had carriers 
in vaccinated animals and in animals that have been 
housed with distemper dogs, but in the ordinary healthy 
dog I have not found the organism. The disease has 
been produced experimentally with this organism—there 
is no doubt about it ; and dogs have been protected against 
infection with both live and dead organisms injected 
subcutaneously—there is no doubt about that either: 
could this be done with an ordinary saprophyte normally 
found in healthy dogs ?” ia 
In the same letter he dealt with the supposition that 
B. bronchisepticus sets up a broncho-pneumonia. which 
