Page 126 - My FlipBook

in progress looking to that end, and although they have not
yet made sufficient progress to be in any wise useful to us
to-day, they are making such progress that we may expect
great usefulness from them some time in the future.
Now, what do we mean by susceptibility and immunity^*
Two persons become infected, or are infected with a certain
pathogenic micro-organism. One of them takes the disease
and is sick—the micro-organisms grow. The other does not
take the disease, is not sick—the micro-organisms fail to
grow, or, if they grow, produce no evil results. The first is
susceptible, the second is immune. Or, again, two children,
apparently in equal health, are exposed to measles ; the one
takes the disease, the other does not; the one is susceptible,
the other is immune. Why? Again, the one that did not take

the disease at the first exposure may do so at the second or
third exposure ; not very susceptible, yet will contract the
disease under favorable conditions for the transmission of
it ; not completely immune. Therefore, we have all degrees
of susceptibiHty and immunity. Some persons are very sus-
ceptible or slightly susceptible to this or that disease, while
other persons are totally immune.
Many of the animals are immune to the diseases of man.
There is only one of the animals that has small-pox, so far as
we now know and that only in a modified form. The disease
is practically confined to man. Cattle have small-pox in a
modified form. None of the animals have cholera, yellow
fever, typhoid fever, measles, etc., diseases that are so com-
mon to man, and some of them so fatal to man ; animals are
immune to these diseases. Why? is the question. Man and
horses have tetanus ; dogs and cattle are immune to tetanus.
Why immune? What are the conditions of this immunity?
None of the animals have caries of the teeth. I think I am
justified in making this statement, for for many years back
I have been looking for caries of the teeth in animals. I
have had many teeth presented to me as specimens of caries
of the teeth in animals, but not in any case have I found, upon
examination of them, that it was caries of the same nature or
seeming to have any relation to caries that we find in man.
Therefore, until some better evidence is presented to me of
the occurrence of caries in the teeth of animals, I feel disposed
to say that caries as we know it as occurring in man does not

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