216 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [VI, III
bovines is not necessarily associated with an elevation of body temperature.
There would thus appear to be some reason for doubt as to whether the parasite
responsible for surra in bovines is referable to the species Trypanosoma evansi at
all, and although in a recent communication, Rao and Mudaliar [ 1934 ] have
produced some experimental evidence to show that this is so, it would seem that
the final solution of the problem will not have been arrived at until further light
has been thrown on the precise identity of the species of trypanosome involved
in the occasional cases of fatal or acute surra in cattle. Should the parasite con-
cerned in cases of this kind actually turn out, as a result of intensive morpholo-
gical studies, to be indistinguishable from T. evansi, then it would be of consider-
able interest to ascertain the circumstances under which this parasite, which is
usually innocuous for bovines, attains the status of a virulent variant for these
animals.
Unfortunately, an investigation into problems relative to bovine surra is ren-
dered difficult by the fact that there is no reliable method for the diagnosis of the
disease itself. A perusal of the available literature shows that practically all
workers are agreed as to the difficulty of diagnosing the disease in ruminants, and
repeated reference has been made by them to the futility of declaring a bovine sub-
ject as free from surra from the mere fact that an examination of its blood smears
has proved negative for the presence of surra parasites, for these may be so scanty
that " microscopical examination of the blood carried out for long periods may fail
to reveal the presence of trypanosomes " and even when the temperature is high
" microscopical examination of the blood may fail " [ Sheather, 1934 ]. The diffi-
culty of diagnosing bovine surra with certainty has also been referred to by Bakker
[ 1925 ] in the Dutch East Indies, while Gaiger [ 1911 ], in India, even declared
that " ordinary microscopic examination of the blood of cattle for T. evansi in
India is useless, the parasites are so few in number that they have never been so
seen ". Several workers have, therefore, mentioned the desirability of diagnosing
surra in bovines by means of the so-called biological tests, that is, by the sub-
inoculation of the suspected blood into small animals [Doeve, 1918; Hornby, 1921;
Sheather, 1934], although Gaiger [1911] would even regard this method of
diagnosis as "obviously impracticable" but feels "almost certain that given
time, money, and opportunities for experiment, other means might be devised ".
In referring to the impracticability of the biological test, Gaiger had presumably
in mind the difficulty of conducting large-scale sub-inoculations under the condi-
tions obtaining in the field when one has to deal with an actual epizootic of cattle
surra.
A reference may be made at this point to four other well-known methods that
have been recommended from time to time for the diagnosis of surra, namely,
Formol-gel [ Knowles, 1924, 1925] and the Mercuric Chloride [ Barnett & Kenny,
1928 ] tests and the method of diagnosis based upon the so-called Adhesion Pheno-
menon [ Davis and Brown, 1927 ; Duke and Wallace, 1930 ]. Apart from the fact