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TYPHO-ID FEVER.                        387

upon the stage of a microscope and examined for the

As recent extended observations have shown that occa-
sionally the blood of healthy men and animals has the
power of producing the agglutinations, the consensus of
opinion now seems to be in favor of the view that a cer-
tain dilution of the blood is required for a satisfactory
diagnosis, and that all reactions with concentrations
greater than one part of blood in fifty of culture may be
questionable, while less concentrated dilutions are almost
positively diagnostic. A time-limit must be placed upon
the experiment. For the weak dilution not mpre than
two hours should be required for a perfect reaction, and
for the stronger solution correspondingly less time should
be required.

A curious fact that should not be overlooked is that the
agglutinating substance is not constantly present in the
blood, but sometimes alternates, being present for several
days and then absent for a day or two.

The agglutinating power of the blood occurs early in
the course of typhoid, and in typical cases seems to be
present in the first week of actual illness.

A point that should not be forgotten is that the agglu-
tination of the bacilli seems to be a phenomenon quite in-
dependent of any immunity possessed by the individual,
and therefore is not an "immunity-reaction." Just what
the agglutinating substance is, has not yet been determined.
The agglutinations are occasionally caused by the
serum and dried blood from other diseases than typhoid,
but in a collection of 4000 cases it was shown that the
errors from this source were only about 5 per cent.

Malvoz l has experimented with a number of chemicals,
and has found that formaldehyd, corrosive sublimate, per-
oxid of hydrogen, strong alcohol, and anilin colors (such
as chrysoidin, vesuvin, and safranin) have the power to
produce the typical agglutinations even in very dilute

1 Ann. de T Inst. Pastettr, xl., 7, 1897.