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FURTHER NOTES CONNECTED WITH THE ETIOLOGY OF SURRA.
The course of this disease (Surra) is characterized by two kinds of periods : (i) Paroxysms,
during which the hæmatozon (Trypanosoma Evansi) is present in varying numbers, from 1 to
350,000 in each cubic millimetre of blood: (ii) Intermissions, during which the hæmatozoon is
absent.
It may be stated, as a rule, that in all animals, the greater the number of hæmatozoa present
in the circulation during a paroxysm, the shorter will be the duration of such period. The
duration of a paroxysmal period in India varies between three and ten days, according to the
animal attacked. In experimental animals (horses), when the disease has been transmitted by
means of a trace of soiled blood placed in a slight superficial scratch, the paroxysms may last
as long as 22 days, but the organisms rarely exceed 400 in each cubic millimetre of blood.
Although during the intermissions of Surra, the most careful microscopical examination of
the blood has failed to discover the presence of a single hæmatozoon, nevertheless during such
a period, lasting five days for instance, if a fresh guinea pig be inoculated with a like quantity of
blood (0 . 3 c.c.) on each of the days making up the period, it generally happens that four out of
the five animals will contract Surra. The blood extracted on the first or second day of the intermis-
sion, is the sample -which fails to reproduce the disease in the guinea pigs. The period of incu-
bation after such inoculation, however, varies considerably in length in animals of the same
species. In one experiment when the blood of the second day of the intermission failed to re-
produce the disease, the latent period in the third guinea pig was 19.5 days, in the fourth guinea
pig 8.5 days, and in the fifth animal 6.5 days, whereas in ordinary inoculations, guinea pigs
injected subcutaneously with soiled Surra blood from the horse, contract the disease in from
four to five days.
Successful inoculations have been made with blood taken from horses, which succumbed to
Surra, up to 18 hours post mortem, but not later.
It has been previously noted, that the changes brought about in the blood by the hæmato-
zopn in Surra cases are—(i) high temperature, maximum 108°F.; (ii) rapid reduction in
the number of red corpuscles in the blood; (iii) an increase in the number of white corpuscles;
(iv) decrease in the number of coarsely granular oxyphile cells; (v) a diminution in the amount
of hæmoglobin concurrently takes place, most marked during the paroxysmal periods.
When a Surra animal (horse) is treated with arsenic, the hæmatozoon disappears from the
blood after a varying amount of the drug has been administered. The body temperature falls
and reaches normal limits, and the animal frequently maintains its condition, sometimes putting
on flesh. The red blood corpuscles increase in number, and again from normal rouleaux, a dimi-
nution in the number of white corpuscles, and an increase in the number of coarsely granular
corpuscles takes place.
Inoculation has been successfully performed with blood drawn from an animal previously
submitted to arsenic for a few days, from whose blood the hæmatozoon was absent; but after the
ninth day of treatment, the immature form of the organism, if such it be, appears to be acted
upon by the drug, for negative results then follow inoculation with the blood of the animal under
treatment. There is, however, a tendency for the Surra hæmatozoon to re-appear in the blood
of the animal subjected to arsenic, after an absence of about 25, 50, or 75 days.
In continuation of the experiments recorded in 1893, viz., the efficacy of repeated
injections of serum, obtained from bovines directly after severe attacks of Surra, when injected
into equines suffering from that disease, further researches were initiated in small animals
(rabbit and guinea pig), the injected serum being obtained from bandicoots [Mus (Nesokia)
giganteus] just previously the subjects of the hæmatozoa. The injections of serum in the
case of the rabbit, seemed to retard the appearance of the hæmatozoon in the blood, for the
average length of the latent period of Surra in this animal was found to be about 8½ days,
whereas in those experiments it occupied an average of 28 days. In the guinea pig the latent
period occupied the usual time, but the injections of serum appear to have been the cause of
shortening the period of life.
Sweat.—In regard to the calculations on sweat in this report, the amount taken was based
on estimations by Grandeau and Leclerc on horses in Europe. From these experiments it was
found that 6.4 lbs. were excreted daily at rest, and 13.4 lbs. when trotting. F. Smith, quoting
Colin, gives 14 lbs. as the probable loss in 24 hours, and this figure has been taken for our
experiments as most probably representing the loss in a tropical climate like Poona. The sweat
figures therefore are not given as scientifically accurate, but are sufficiently close to only interfere
very slightly with the other questions at issue:
In the case of the mules an average of 9.6 lbs. daily was taken. All the animals under
experiment were thoroughly groomed twice daily.
Digestion.—A voracious appetite is one of the marked systems of animals suffering from
Surra, and they frequently die with their mouths full of grain or fodder. In the three cases
under experiment, viz. Horse No. LXXXIX (2nd Series) and Mules I and II, the digestive