8
preventive measures had been discovered, 90 per cent. of the whole of the
cattle of South Africa would have been carried off within a very short time,—
the seriousness of which it is difficult to form any idea in a country in which
both agriculture and, to a large extent, means of communication are dependent
on these animals. It is obvious that under such circumstances the only
measure that would stem the plague was to pass as many as possible of the
animals through a mild form of the disease, so as to produce in them an
immunity that would last for a life time. It was for this reason that
Koch's bile method, which had been of the greatest service before more
lasting ones were discovered, has now given place to the serum
and glycerine bile methods.
In India, however, the conditions are totally different, for here the disease
has been present for centuries, and consequently a certain degree of immunity
has been gradually acquired, so that the disease is usually rather of an endemic
than of an epidemic type, and is attended with a lower mortality, and has much
less tendency to spread widely and rapidly than was the case in South Africa,
although at times it assumes a more epidemic character as was the case in
Manbhoom District in the year 1861-63, when 75,000 cattle were reported to
have died of this disease, and in Assam in 1852-53, when 120,000 were carried
off. However, although this disease is more or less constantly present in every
part of India, yet in most districts only a few villages are attacked each year,
so that the odds against any particular village in which the disease may be
found being attacked again within the next ten or twenty years may be great,
and consequently experience may prove that an immunity which is sufficient to
check any particular outbreak, say, one of a few months' duration, is all that is
required. Once more the breeds of cattle in South Africa differ widely from
those of India, and those of the latter country differ widely from each other, so
that, before carrying out methods of inoculation on a large scale, careful experi-
ments are required. For instance, it is well known that when the disease appears
among Hill cattle, it is usually of a very virulent nature, and may carry off as
much as 90 per cent of the animals attacked, while in the Plains it is not as a
rule nearly so fatal. In correspondence with this difference in susceptibility it
has recently been found in this Laboratory that Hill cattle require a much
larger dose of serum weight for weight for their protection than do Plains cattle,
so that the whole question requires to be carefully tested experimentally before
final conclusions as to the best method to adopt in this country are come to.
Taking into consideration the above mentioned points, it may be said that
what is most wanted is a method which will produce an immunity as rapidly as
possible, as the outbreaks will seldom be reached until they are at their height,
while, if it is to gain the confidence of the villagers, care must be taken not to
run any risk of any material mortality among the inoculated cattle, or of a too
severe degree of illness, even at the expense of a less durable immunity, which
is of much less importance in this country than it was in South Africa, for the
reasons already pointed out. The religious susceptibilities of the people must
also be reckoned with, and for this reason alone the bile method of Koch, which
necessitates the slaughter of some 7 per cent. of the animals, at from the
sixth to the eight days, in order to obtain bile for the protection of the others—a
protection, moreover, which is only a temporary one,—is practically out of the
question in India. I am aware that this difficulty may be overcome to some
extent by the use of buffaloes for obtaining the bile from, but this involves a
further loss of time in obtaining and inoculating these animals if there are none
of them affected in the village, while both the expense and the period before the
immunity is produced will be much greater than in the serum method. The
glycerine bile method gets over the difficulty of slaughtering animals, but at the
expense of a still greater delay, as after the bile has been obtained it must be
glycerinated and kept for eight days, and ten days later again the animals must
be inoculated with a small dose of virulent blood, and are still susceptible to
natural infection for some days longer,—a very serious drawback, for it is usually
quite impossible to separate the infected from the uninfected animals in an effi-
cient manner in Indian villages. The necessity of inoculating all the animals
a second time ten days later will also be a serious drawback in Indian
villages where the simplest possible method will be most likely to win the
confidence of the inhabitants.
It would appear, then, that if the results obtained in South Africa are con-
firmed in India, that the serum method, or a modification of it, so as to give but