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200 THE MICRO-ORGANISMS OF THE HUMAN MOUTH.

subsist principally on meat, we arrive at quite different conclu-
sions. The animals referred to are such as live on the same food
as civilized human beings, especially dogs and other domesticated
animals that feed on substances which form acids by fermenta-
tion.
All writers on this subject are, I believe, unanimous in the
opinion that decay is exceedingly rare in the ease of carni-
vora.
Bland Sutton, who has occnpied himself with this study for
many years, found only a small number of decayed teeth in car-
nivora, and these almost invariably in animals living in captivity
for some length of time.
I have obtained information confirming these observations
from the directors of various zoological institutes and veterinary
colleges.
On the other hand, according to my experience, every consid-
erable collection of dogs' skulls will be found to contain one or
more decayed teeth, nor is decay of very rare occurrence in
horses and apes.
In two hundred and ninety-five dogs' skulls, mostly of bull- and
lapdogs, I found eighteen cases of decay ; in six, two teeth were
decayed; in each of the remaining twelve, one. In two other
cases probably incipient decay (I could not decide with cer-
tainty whether the teeth were really decayed or not); these two
are therefore not included in the above number. In all these
cases it was invariably the first upper molar that was decayed^
which is explained by the fact that this tooth possesses deep
retaining-points for food-particles on the grinding-surface. The
fourth bicuspid also frequently showed signs of decay, but no
cavity. Decay occurs in these skulls in the proportion of 6 : 100,
which signifies much higher percentage than has been found in
Esquimaux and various Indian tribes. I succeeded in obtaining
material from the dry, decayed tooth of a dog, which being
soaked for a few hours in water, and then cut on the freezing
microjtorae and stained with fuchsine, yielded very fiiir micro-
scopic specimens. Through these specimens I was enabled to
establish the interesting fact that decay of dog teeth is accom-
panied by exactly the same phenomena as that of human teeth