Page 790 - My FlipBook

800 DENTAL CARIES. ;

of lactic acid is boiled, a small fraction of the acid goes over with the
water. To ascertain, however, whether any other acid, especially vola-
tile, was present, the distillate was boiled with carbonate of lime,
filtered, evaporated to dryness, a small amonnt of dilute sulphuric
acid added, and heated in a retort over the water-bath. A few drops
of an oilv acid came over, which when taken upon the fingers smelled
like butyric acid ; the amount, however, was so small that no attempt
could be made to analyze it.
I have been able with some degree of certainty to establish the pres-
ence of lactic acid in carious dentine by a method theoretically so
simple that it seems strange it has never been made use of before, but
which, however, in practice, is carried out only with great difficulty.
My first and second attempts were only partially successful ; the third
succeeded sufficiently well to justify its description here.
In this experiment I made use of fifteen teeth, all containing consid-
erable quantities of carious dentine, and all extracted on the day of use.
The remains of food were first removed from the cavities, but none of
the softened dentine ; then all the softened dentine was taken out and
placed in a porcelain vessel, cut or picked into fine pieces, placed in a
test-tube with 1 c. c. of water and two drops of a lO-jier-cent. solution
of hydrochloric acid added. Any free la(:tic acid in the carious den-
tine would remain free, and any existing in combination with lime
would be set free by the hydrochloric acid. It Avas then gently shaken
with about 25 c.c. sulphuric ether, and the latter, holding the lactic acid
in solution, was after some minutes j)oured off into a second test-tube
here it must be allowed to stand fi'om twenty-four to forty-eight hours,
till it becomes perfectly clear. It was then filtered into a porcelain
dish, evaporated, a few drops of distilled water and a small quantity of
freMy-prepared zinc oxide added, gently boiled (water being added as
necessary) for ten minutes, the three or four dro})s of liquid remaining
filtered on to a glass slide and allowed to crystallize. I obtained the
forms seen in Fig. 410. Their close resemblance to
Fig. 410.
^^iQ crystals of the lactate of zinc (Fig. 409) will be
seen at once. There can, in fact, scarcely be a doubt
that they are lactate-of-zinc crystals. The lactic acid
concerned in their formation must, of course, have
existed in the carious dentine.
I have noticed in the dental journals a tendency on
the part of some writers on this subject to derive a
large amount of satisfaction from the statement that,
after all, what I have done to clear up the subject of dental caries was
done and known long ago. One writer even states that he might
almost have said two years ago something that I said but a few months
since. Let me say, once for all, that I have too little sjiare time to
devote any of it to the discussion of the (jue.stion who said this or that
first, or even who mir/ht almod have said something two years ago.
There is perhaps no human disease about which more has been said
than about caries of the teeth ; and when the subject shall have received
its final settlement, there will be hundreds Avho may say, " I told you
so." Malassez and Vignal very justly say of Baumgarten, who claims