24
REPORT OF THE IMPERIAL INSTITUTE OF VETERINARY RESEARCH,
In the past, it has been difficult at the laboratory to devise methods for demonstrating
the potency of a serum, but with the use of hill bulls as test animals and titrated dosages
of very virulent culture the process of testing has now been found capable of systematiza¬
tion, and hence the optimum methods of serum manufacture may be resolved upon.
In order to prolong the immunity conferred by serum alone the procedure that has
to be applied is to inoculate simultaneously a culture of suitably degraded virulence,
according to the method originally advocated by SOBERNHEIM, and although this method
of immunization has not been practised in India it would seem a priori to be a system
particularly well suited to the conditions in which protection of livestock against anthrax
is presented as a problem to the veterinary authorities. There seems no difficulty now
in the preparation and despatch of strains of anthrax culture of the desired virulence for
inoculation. Some remarks are appended in the section dealing with Research on the
work done upon vaccination at the laboratory. Some of the anthrax serum was issued
from the laboratory for treatment, including the treatment of human clinical cases of the
disease.
(e) Mallein. The products now issued from the laboratory for testing equines for
glanders are of two kinds, namely, (i) " ordinary " mallein, for the subcutaneous test
and (ii) special mallein, for the " intra-palpebral " (" intra-dermo-palpebral," or,
" I.D.P.") test. The latter form of test gained considerable favour with the Army
Veterinary authorities during the War on account of the relative ease with which it
could be applied, and has since retained to a large extent its popularity. Although
the manufacture of mallein is a pursuit which has behind it the experience of first-
class laboratories for many years, yet one cannot find published in connection with
it much that will guide one in turning out regularly " brews " of unimpeachable efficacy.
The recent investigations, notably of WATSON in Canada, would appear to show that
a good deal of the mallein placed on the market is of low quality, or even useless for the
purpose of testing. Following upon reports from the field that some issues of mallein
did not provoke distinct signs of reaction in animals that were subsequently found to
be glandered, the routine processes of manufacture were closely studied in order to ensure
uniformity in the quality of the product made from time to time at the laboratory. The
method of testing the various " brews " prepared for these studies was always the direct
one, upon horses artificially infected with glanders (by feeding). The " brew " under
test was injected subcutaneously (side of neck) and intra-palpebrally on one side of the
animal, and the same quantities of a mallein manufactured by one of the foremost labora-
tories in Europe on the other. It was found that the mallein prepared from cultures
grown in ordinary glycerinated peptone broth gave irregular results, and although attempts
were made to prepare the broth in a uniform manner, it was not always conducive to the
development of the properties after growth in it of the glanders bacillus that set up un-
equivocal signs of reaction on injection into glandered horses. The poor " brews"
appeared to be those exhibiting a marked initial lag and relatively meagre development
of the bacterial growth. It has been believed by some workers that concentration by
evaporation leads to a more effective extraction of reactive substance from the bacterial
bodies, presumably through the action of the higher concentration of glycerine, and that
the mallein that was used for the " I.D.P." test acquired its special efficacy through
concentration prior to subsequent dilution to a certain strength. Also, according to the
experience of some laboratories the maintenance of a high degree of virulency, by passage
through animals, is necessary in a strain of the glanders bacillus used for the preparation
of mallein. The strain used at the laboratory now, isolated many years ago from a
country-bred pony, is indeed passed from time to time through guinea-pigs, mainly to
ensure its purity, but there is nothing to indicate that the efficacy of the mallein prepared
is in any way allied to the virulence of the germ employed for making it. Again, tests
failed to reveal any advantage in concentrating relatively poor cultures in order to obtain
from them a better mallein.
The experience of this institution now indicates that the essential requirement for
the preparation of a good mallein is the employment of a good broth, in which the glanders
bacillus develops with hardly any appreciable period of lag and gives rise to a rich growth
which attains its maximum in two or three days at body temperature ; incubation at
this temperature is necessary subsequently for about three weeks, to bring about the
autolysis of a large bulk of bacterial substance, and it is this process which apparently
liberates the reactive properties. After a number of trials broth made up in the manner
of the culture medium used for the growth of the hæmorrhagic septicæmia organism,