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from the other when both are found in the saHva, which is
frequent. When this organism is present in the culture it
will usually show itself in white points, almost milky in ap-
pearance ; occasionally it will be mingled with the caries fun-
gus and give the culture a grayish appearance. It grows more
xapidly in artificial culture than the caries fungus, and will
soon overrun the latter. In plate cultures the colonies are
readily distinguished from those of the caries fungus, by their
lighter color and larger size, and if on gelatine they will lie in
a pool of liquefied gelatine. The caries fungus does not
liquefy the gelatine. Exceptionally, even with very careful
work, the cultures will be contaminated wdth various micro-
organisms. The caries fungus is not a good grower in arti-
ficial culture, and other micro-organisms are very apt to over-
run and obscure it.
Caries fungus is the most constant of the micro-organ-
isms in the saliva. In all of my experimental cultivations I
have never yet found a person who had not this organism
plentifully in the saliva. It is found in all parts of the mouth
and apparently grows much more rapidly in its natural sur-
roundings than in any artificial medium. In most cases it is
found free in the saliva, upon the mucous membranes, or about
the teeth, with or without gelatinous coatings, or it is com-
mingled with masses of other micro-organisms. There are
conditions, apparently, of the saliva, in which it grows plenti-
fully without the formation of gummy material, and there are
other conditions in which it forms much of this, in which it
will be found imbedded. This material is almost as trans-
parent as glass, but has a slight yellowish tinge when in large
masses, as sometimes obtained in artificial culture. I have
several times obtained masses of it as large as a filbert, grown
in 15 c.c. of broth. The best way to observe this in the
mouth is to look for it in young persons in whom buccal or
labial decays are starting, and whose mouths are habitually
fairly clean. Upon the buccal or labial surface of a tooth that
presents a slight whitening there is pretty sure to be a fairly
pure gelatinous plaque, i. e., not greatly mixed with other
micro-organisms. Wash this with a stream of water from the
syringe, and then take a sharp, broad blade, and, beginning
at one margin of the area of liability, carefully peel up the
plaque. At first nothing will be seen, but as the peeling pro-

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