168
Contagious Abortion of Cattle, Sheep and Goats
[VOL. XVIII, PART III,
Conditions of experiment in fig. 5.
Vehicle. As for fig. 4.
Storage. As for fig. 4.
Suspension. As for fig. 4, but the suspension was washed before use by centrifugation and
resuspension in the same vehicle once.
Note. The drift of pH during the course of the experiment was as follows:
Test A. pH 5.4 to 5.6
B. pH 6.0 to 6.2
C. no change.
Table of counts in hundreds of millions per c.c.
Hours
0 . . . . . . . . . . .
20 . . . . . . . . . . .
26 . . . . . . . . . . .
32 . . . . . . . . . . .
42 . . . . . . . . . . .
52 . . . . . . . . . . .
66 . . . . . . . . . . .
pH 5.4
102.0
7.7
6.3
6.0
1.9
0.97
0.07
pH 6.0
124
89
56
65
34
23
4.9
pH 6.8
124
80
68
67
39
34
2.4
At this point, the poor keeping qualities of the Brucella vaccine in the Indian field were reconsi-
dered. In an earlier experiment (Table XL) counts, made on vaccines sent to the Military Veterinary
Laboratory, Lahore, stored for varying periods at average temperatures of 71° and 77°F. and returned
to Mukteswar, compared very unfavourably with counts on a control vaccine stored at a constant
79°F. in the Institute. Therefore, as temperature alone was clearly not to blame, it appeared that
death might have been due to (i) changes in temperature during transit or (ii) shaking during transit.
In experiment V, Cotton's strain 19 was suspended at density 5 (Brown's scale) in the optimum
vehicle evolved in Experiments I to IV (i.e., 0.85 per cent NaCl in glass-distilled water, buffered with
M/50 Sorensen's phosphates to pH 6.4, with the addition of 0.1 per cent tryptose). This suspension
was divided into three parts ; one portion was stored continuously at 42°C., a second sample was moved
from one incubator to another, so as to vary the temperature of storage as much as possible, whilst
roughly imitating the diurnal temperature changes on the plains (see schedule on the reverse of Fig.
9.) A third sample was shaken from 10 a.m. to 4-30 p.m. and throughout the night was stored
at 42°C. without agitation. The shaking was achieved by placing the suspension in a bottle which
contained 3 parts of air and 1 part of vaccine and attaching the bottle to a rotor moving in a plane
set at approximately 30° to the vertical. In this way the vaccine was precipitated from end to end
of the bottle, twice in each revolution. The speed of rotation was 120-150 r.p.m. As may be seen
from an inspection of Fig. 9, the bacterial death-rate was not strikingly affected by shaking and not
at all by variations in temperature. A puzzling result, for not only is it at variance with the inference
drawn from the mortality occurring during transit in India, but it also disagrees with the findings
of Mitchell and Moore [1942], who, by means of counts taken before and after various journies, de-
monstrated the lethal effect of trnasportation on Brucella.
Nevertheless, it must be recalled that in the foregoing experiment the control remained for the
whole time at 42°C. whilst, during the shaking periods, the shaken sample was at bench temperature.
Thus, as the two mortalities are almost the same, it is to be supposed that bacterial destruction due
to shaking at say 22° to 25°C. equals that due to storage at 42°C. Moreover in this experiment the