March, 1953]
J.
M.
LALL
AND
N.
C.
SEN
35
could be replaced with fresh vaccinated stock within a period of say four years, the
oldest animals being eliminated as fast as young vaccinated animals become available
to replace them. Once the turn-over of the milking stock was complete, it would not
be necessary to carry out vaccination any further, rather in their turn during the
following four years, the vaccinated animals would be replaced with non-vaccinated
ones. In this manner non-reacting, tuberculosis-free herds might be established with
a minimum interference with farm management and to our mind this only seems to
be a practical and realistic procedure for our country, where slaughter of cattle for
beef purposes will not be a desired course on sentimental grounds.
How far does the vole bacillus satisfy the requirements for a vaccine likely to
succeed when employed for the above Plan? Young and Paterson [1949] have
shown it clearly that a single dose of 5 mgm. given intraveneously was capable of
inducing in some animals a very marked degree of resistance for periods up to three
years and possibly longer, but such a degree of resistance was not seen in every case.
So it seems very necessary to look for some way of intensifying the initial resistance
either by increasing the dose or attempting revaccination. The former course does
not appear to be a practical proposition as the dose used by Young and Paterson
seems to be the maximum tolerated by the animals with safety. Regarding repeated
vaccinations, the limitations of such procedure should also be borne in-mind, as this
would entail periodic dislocation of the routine of farm management. However, if
sufficiently strong resistance could be produced and a practicable plan of eradicating
tuberculosis could be demonstrated to the livestock owners, they will not hesitate
in handling it even if there be some economic loss to them and perhaps it will not be
very difficult to enlist voluntary support for meeting the loss from the philanthro-
phists of our country, who hold cow with such a great reverence.
Young and Paterson [1949] observed that revaccination after intervals of time
varying from four weeks to six months after primary vaccination did increase resist-
ance to infection but nothing was so far known if the resistance could be prolonged,
and if so what would be the optimal revaccinating dose and the optimal period
between vaccinations. Some other important connected problems (as suggested
by Young and Paterson), awaiting detailed investigations and which would lead to a
closer understanding of the principles underlying immunization against tuberculosis
are:
(i) histological studies of the affects of revaccination on the cells of the reticulo-
endothelial system to find out that revaccination can lower or in-
tensify resistance according to whether the revaccination is carried
out during the period, when the cells of the reticulo-endothelial system
are in an irritable state or delayed until the activity of the cells has
subsided.
(ii) the study of the functional activity of the endocrine glands.
And, yet another very interesting and very useful field of study will be to see
if smaller doses of the vaccine would prove effective if given in combination with a
vaccine consisting of ultra-violet killed virulent bovine bacilli or comparatively
virulent vole baccilli or suitable extracts of these bacilli. Perhaps they may bring
about a state of resistance in which the cellular and humoral factors are more evenly
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