SEPTEMBER, 1948]
JOHN
B.
POLDING
135
systemic disturbances. More remotely, it may be supposed that many buffalo abortions are not
due to Brucellosis at all, but to some quite unrecognized factor of rainfall, a preposition which receives
further consideration on page 188.
Plainly, the dissemination of Brucella in India is influenced by several interdependent factors
and, while it is not possible wholly to disentangle their individual roles, some tentative postulates
come to mind. The factors which inhibit fruitful dissemination are elementary hygiene, sunshine
and animal dispersion, and where indigenous cattle are concerned, the optimum action of all the three
will result in a gradual elimination of the disease, or prevent its gaining a hold on an already clean
farm. Further, the combined action of any two factors is likely to minimize the disease, but, where
one factor alone is operative, the disease will in all probability spread. Conversely, the influences
propitious to dissemination are absence of hygiene, absence of sunshine and congestion.
The conflicting roles of humidity and dryness are less ponderable, but at least it is easier to clean
dry hard surfaces, than wet and muddy ones, while the vehicular value of fluids cannot be
ignored.
Many epidemiologists have associated moisture with the spread of diseases. Rogers [1926],
for example, found that cholera spreads as the absolute humidity reaches 0.4 in. and it may be noted
in passing that, in lower Bengal and on the Coromandel and Malabar coasts (i.e., in the Brucella
endemic areas of India), the absolute humidity is never below 0.4 in.
About Brucella little has been proffered, but Horrocks [1905] found that these organisms sur-
vived for 43 days, in soil that was allowed to dry naturally (in Malta) and for 72 days in damp soil.
Be that as it may, whether soil-moisture, the relative or absolute humidity of the atmosphere, or a
tri-seasonal rather than uni-seasonal rainfall is considered, the main function of the moisture will
be to delay or obviate drying. Consequently, the effect of drying Brucella has been studied in one
or two simple experiments.
In one series of tests, 0.5 cc. of a Brucella suspension in saline (density=Brown's scale 5 ; approxi-
mate live count=10,000 million organisms) was pipetted on to filter papers previously placed in
lightly plugged test tubes. A 1/10 dilution of the suspension could be reconstructed from these
papers by pipetting 4.5 cc. of saline into a still-wet filter paper, or 5.0 cc. into a paper that had dried.
Re-suspension was effected by pulping and wringing the paper with the pipette. The resulting
suspension was used to make a ten-fold rising dilution series for counting. Later, this technique was
abandoned, as unevenness of the paper pulp caused irregularity of counts.
Using this method, the effect of rapid drying in vacuo was studied. Attached to a Chryochem*
apparatus and subjected to a vacuum of 50µ the papers took about 1 hour to dry. No artificial
freezing was used but self-freezing may have occurred towards the end of the process. The suspen-
sion was counted before placing on filter paper, again after reconstruction immediately after deposi-
tion on the paper and finally immediately after drying. The results of duplicate counts are shown in
Table XXIV and reveal that a large number of Brucella die during rapid drying under vacuum,
even at room temperature (20-25°C).
TABLE XXIV
The survival of Brucella during rapid drying (Chryochem apparatus)
Nature of suspension
Saline suspension at the time of preparation . . . . . . . . .
Suspension reconstructed from wet filter paper immediately after wetting
.
.
.
.
Suspension reconstructed from filter paper immediately after drying
.
.
.
.
Count in millions per cc.
Trial I
6,300
3,000
150
Trial II
4,400
3,800
190
* (Flosdorf-Mudd (1938) method) F. J. Stoks Machine Co., Philadelphia, U. S. A.