120
[CHAP. III., ΡT. II.
figures—spindle, dumb-bell or disc-shaped—some of these being many times larger than the
original bacilli. Such appearances are known as " involution forms," and in the early days
of plague bacteriology, they were considered to le very important from a diagnosis point.
of view. (Vide Plates III. and IV.)
A number of cultures were however found by Mr. Haffkine which did not show these
appearances ; and he afterwards found, in an enquiry made together with Major Bannerman,
that these appearances belong to microbes taken recently from plague patients and that they
gradually lose them in the course of cultivation in the Laboratory.
Mr. Hankin and Gapt. Leumann aver that these forms are produced moat readily by
employing Agar to which an excess of salt has been added. Mr. Haftkine finds, however,
that they are equally demonstrable, in cultures of bacilli taken direct from the body, on
ordinary Agar, if it is "dry " and has a definite alkaline reaction : and adds that involution
forms are most readily demonstrable on old and dry Agar, especially when it is inseminated
very abundantly ; and that they are never seen in liquid cultures, but can be observed in
the tissues of animals.
Captain Childe reports that similar "rounded or swollen" forms are to be found in the
tissues of the human body, if the examination be made from 5 to 12 hours after death ; the
change being, in his opinion, a post-mortem one. Mr. Haffkine had previously found such
forms in the body of a rabbit, and suggested that they might be present in human bodies also.
The bacilli cultivated in Bouillon show a tendency to form short chains of 5 or 6 bacilli
(vide Plate Y.)—each chain showing generally a slight but very remarkable bend : but this
latter characteristic is not yet perhaps fully established. They also stain evenly and very
deeply, -but in old cultures most of the bacilli disintegrate and they do not then take the stain
well.
Biology and cultural
characters.
The plague-bacillus forms characteristic appearances on most of the common media.
In India, for general work, preparations of Agar-agar are
usually employed. Gelatine liquefies at the ordinary tempera-
ture of hot climates, and cool incubators, etc., are necessary for its use.
Growth in Bouillon.
Haffkine's Stalactites.
In ordinary faintly alkaline or neutral peptone bouillon, and especially if a few
drops of oil or fat (ghi, cocoanut, olive, or linseed oil)
are added to it. the appearances known as "Haffkine's stalactite
growth will be seen. Ten to twelve hours after insemination a diffuse cloudiness due to the
universal growth of the bacilli throughout the liquid is to be observed. The diffuse cloudi-
ness disappears later on, and colonies of bacilli are to be seen hanging from the surface in
stalactite form, sometimes reaching to the bottom or sides of the flask to which they may be
attached. These colonies, thin, and more or less numerous at first, quickly increase in size and
number so as to form a thick jungle of stalactites. This appearance is, so far as we know at
present, absolutely diagnostic of plague. Sometimes no stalactites are to be seen in the begin-
ning, but white spots, due to the zoogleic masses of bacilli, appear on the sides of the flask
and on the surface of the liquid. Later on, when the stalactites appear, these white
masses of growth are found to correspond to the points of attachment of the stalactites.
(Vide Plate VI.)
This stalactite growth is very fragile, and for its proper development requires that the
bouillon be kept absolutely at rest. A solid table in a dark room on the ground floor should
therefore be chosen for the resting place of the culture flask ; and a convenient method of
displaying the growth is to hold a light behind the flask and to look through the fluid from
the opposite side.