42 KENNEL DISEASES. 
advanced that the disease is caused by a micro-organism, it was for a long time 
stoutly resisted. However, at the present time this is generally accepted. Yet 
there are many physicians who are not wholly reconciled to it ; and while believ- 
ing that the vast majority of cases of pneumonia are of germ production, these 
think that there are occasional instances in which the disease, varying some- 
what, perhaps, in character, is caused by other influences, as a sudden fall in 
temperature, mechanical injuries, etc. 
The advocates of the germ theory meet such objections with the plea of 
susceptibility; that is, that cold, damp, sudden changes in temperature, electri- 
cal influences, etc., all of which have been considered exciting causes of pneu- 
monia, are not so, but simply what physicians term predisposing causes. In 
other words, those influences render all more susceptible to the disease, the 
lungs then being a more fertile soil for the special germ. 
This theory that pneumonia is a germ disease and therefore infectious is by 
far the most probable one, and evidence to support it is steadily accumulating. 
Certainly in no other way is it easy to explain epidemics, or the resemblance 
between the pneumonia of man and the contagious pneumonia of cattle, which 
is well known to be essentially epidemic and transmissible by contact and 
inoculation. 
Very evidently cases of pneumonia differ much in the matter of infectious- 
ness, and that some are far more infectious than others. Cases differ greatly also 
in intensity, some of the attacks being mild and quickly recovered from, while in 
others death occurs within two or three days. If pneumonia is a germ disease, 
the reason for this variability would appear, for where germs are the cause, the 
grade of the disease is largely in accordance with their number and virulence ; 
and in mild cases it may be accepted that the patients have taken into their 
systems either a small number of germs or germs not especially virulent, or 
their susceptibility to the germs is not great. 
No small number of scientists in their practice among mankind have for some 
years made careful investigations, and found a peculiar bacillus always present in 
their cases of pneumonia. This has been cultivated and experimented with by 
some, who claim that an outbreak of pneumonia may be prevented by protective 
inoculations; while the disease, even when it has been on for a time, may be 
cured by the same means. IE this is so, — and there is scarcely reason to doubt 
it, — microscopic researches will likely soon uncover the germ of pneumonia of 
dogs, and prevention and cure be as possible with them by like methods. 
While the question as to the nature of pneumonia is under discussion, the 
reader will do well to assume that it is infectious, and set his course accordingly, 
if he is so unfortunate as to be called upon to care for a case of the disease. At 
the same time he can safely accept that it is not markedly so in any instance ; 
and that even in the most virulent cases there is but little danger of its being 
transmitted if a few reasonable precautions are taken. 
