83
FURTHER REMARKS ON THE ETIOLOGY OF SURRA.
The course of this disease is characterized by two kinds of periods (i) " Paroxysms ", during which the Paroxysms and
hæmatozoon (Trypanosoma Evansi) is present in varying numbers, from 1 to 350,000 in each cubic millimetre of intermissions,
blood.
(ii). "Intermissions ", during which the hœmatozoon is absent from the circulation.
Duration
of-
paroxysm, influ-
enced by number
of hæmatozoon
present in the
blood.
It may be stated as a rule that in all animals, the greater the number or hæmatozoa present in the circulation
during a proxysm, the shorter will be the duration of such period. The duration of a paroxysmal period in
India varies between 3 and 10 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 superficial scratch on the muzzle, the paroxysms may last as long as 22 days, but the organisms rarely
exceed 400 in each cubic millimetre of blood.
Blood during
intermission has
power to repro-
duce the disease
when
inoculat-
ed under certain
conditions.
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 five of the animals will contract Surra. The blood extract-
ed on the first or second day of the intermission is the sample which fails to reproduce the disease in the guinea-
pig.
Period of incu-
bation of Surra
varies according
to the day of in-
termission.
The period of incubation 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 reproduce the
disease, the latent period in the third animal was nineteen point five (19.5) days, in the fourth animal eight
point five (8.5) days, and in the fifth animal six point five (6.5) days, whereas in ordinary inoculations, guinea-
pigs injected subcutaneously with 0.3 c. c. soiled blood from the horse, contract Surra in from four to five days.
Post-mortem
blood of diseased
animal virulent.
Successful inoculations have been made with blood taken from the heart of horses which succumbed to
Surra, up to 16 hours post-mortem, but not later.
Changes
in
blood due to the
presence of the
Surra
hæmato-
zoon.
It has been previously noted that the changes brought about in the blood by the hæmatozoon 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 marked diminution in the amount of hæmoglobin concurring takes place, most marked during
the paroxysmal periods.
Effect of arse-
nic on the hæma-
tozoon of Surra.
When a Surra animal (horse) is treated with arsenic,—if the disease is not too far advanced—the hæmato-
zoon disappears from the blood after a varying amount of the drug has been administered. The body tempera-
ture 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 form normal rouleaux, a diminution in the number
of white corpuscles, and an increase in the number of coarsely granular corpuscles takes place.
Effect of arse-
nic on the hæma-
tozoon and im-
mature form of
the Surra hæma-
tozoon.
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 hæmatozoon—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 organism to reappear in the blood of the animal subject to Arsenic, after an absence of about
twenty-five, fifty or seventy-five days.
Whether
any
deterrent effect
produced by the
injection of blood
serum
(bandi-
coots) into ani-
mals before or
subsequent to in-
oculation
with
the Surra hæma-
tozoon.
In continuation of the experiments recorded in 1893, viz.:—As to 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, guinea-pig), the injected serum being ob-
tained from bandicoots (Mus (Nesokua) giganteus) just previously the subjects of the hæmatozoon. The injec-
tions 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 eight and a half days,
whereas in these experiments it occupied an average of twenty-eight 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.
Excretion
of
urea during par-
oxysms and in-
termissions
of
Surra.
It is very difficult to draw definite conclusions with regard to the excretion of urea in the paroxysms and
intermissions of Surra, owing to the fact that the maximum amount of urea is passed at varying times after
the highest temperature has been reached.
The maximum temperature sometimes occurs in the middle of a paroxysm, when as a rule, the urea would
be recorded during that period, whilst at others the highest temperature occurs just before the disappearance of
the hæmatozoon, i.e., at the end of the paroxysm, in which case the maximum amount of urea appears in the
succeeding intermission.
Excretion
of
hippuric acid.
With regard to the presence of hippuric acid in the urine of the horse* and mule, it will be noted on refer-
ence to the accompanying table that in health and at rest the amount of this acid excreted varied very greatly
in quantity, and in two animals (Nos. 91—96) was absent altogether. In the same horse (No. 89) in different
years, but having almost the same amount of exercise the hippuric acid ratio was as 1: 2. In the mules under
observation the amount varied as 1: 19.74.
During the latent period the hippuric acid excreted by the untreated animals increased in amount in 3
out of 5 cases, but it remained stationary in one and the quantity decreased in one animal. In all five animals
however there was a decrease from that observed in the latent period during both paroxysms and intermissions.
In those animals treated after inoculation the effect produced by the administration of arsenic was the
reverse of the above, for considerable quantities were passed during the paroxysms and intermissions of the
disease.
The effect of the preliminary treatment on horses Nos. 98 and 99 with arsenic and the double iodides
of arsenic and mercury, was to reduce the amount of hippuric acid from 3.1 and 1.5 respectively to 1, and to
stop its excretion eutirely during the remainder of the periods which occurred before death took place.
In the case of the horse (No. 89—1st series) which received the double iodides during convalescence from
Surra, the effect produced was to reduce the amount of hippuric acid excreted during the administration of the
drug, but when the iodides were discontinued, the excretion ceased altogether for a considerable period, viz.,
163 days.
* Smith states that in England horses at rest do not excrete hippuric acid in the urine.