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382                 PATHOGENIC BACTERIA.

ating  power  upon bouillon  cultures  of   its  respective

Loffler and Abel also prepared a colon serum which
exerted a like specific action upon the colon bacillus,
but was without effect upon the typhoid bacillus.

The serum of immunized animals has been found to
destroy the motility of the typhoid bacilli in a few mo-
ments, and to cause them to group together. Widal
found that the serum of convalescents and of individuals
suffering from the acute disease possessed the same power,
and suggested that this specific action might prove a val-
uable adjunct in diagnosis.

Wyatt Johnston1 and McTaggert worked upon the
subject, and found that a drop of blood from a typhoid
patient, dried upon paper and kept for some time, when
moistened and brought in contact with a culture of the
bacilli was still potent to bring about a characteristic
effect. When such a preparation in the u hanging drop "
is watched under the microscope the typhoid bacilli are
found to be paralyzed in from one minute to half an
hour, and subsequently to collect in masses—agglutina-
tions. This reaction may occasionally be brought about
by normal blood if insufficiently diluted, but is charac-
teristic enough to be very useful in the diagnosis of ob-
scure cases. In a later paper Johnston states that to ob-
tain a satisfactory reaction an attenuated typhoid bacillus
is more useful than a highly virulent one.

My own experiments have satisfied me of the value of
the test, both for making a diagnosis of the disease and
for confirming the species of the bacillus in doubtful

It is now the opinion of all observers that cessation of
motion and agglutination of the bacteria, resulting from
the contact of typhoid bacilli and typhoid serum, are
inconclusive for diagnostic purposes unless the reaction
follows the combination of a suitable culture and a
definite quantity of serum.

1 Montreal Med. Journal, March, 1897.