NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
18
add that in many of such recorded operations no attempt whatever was made
to show by search in the houses that the number of anopheles was really
diminished. In the present experiment operations against the larvæ might have
been considered most successful if the destruction of breeding-places only was
taken count of, or if popular opinion as to the presence of mosquitoes was con-
sidered evidence. It was, for instance, common in the present y ear to hear that
mosquitoes had almost disappeared. The remark was, however, as often made
by people living outside the area as by those within, and in any case referred obvi-
ously to Stegomyia which, from its habit of biting in the day, calls special atten-
tion to itself. (See operations against culex.)
I may here call attention to some experiments directed against the breed-
ing-places of culex. In the course of the periodical examination of the bungalow
section, attention was given to the breeding-places of culex (C. fatigans,
S. sugens, and S. fasciata), and a large number of collections of waste water, and
water in tubs, tins, and especially in pots were oiled or emptied. All stray tins or
pots were inverted, broken, or removed. By these operations—which required
little or no labour—the number of breeding-places was greatly reduced. Though
no means were taken to show whether culex adults were much diminished by
these means, yet from a number of observations I was led to surmise that Culex
fatigans and stegomyiæ, especially the former, were much more readily reduced
in numbers than were anopheles. Close by the Royal Artillery barracks there
were, for instance, a number of shallow earthenware pots used for horses. A
long row of these was left unused and became filled with rain after each down-
pour. There were, moreover, no other breeding-places for culex found in the
immediate neighbourhood. In the beginning of the season larvæ of C. fatigans
and Stegomyia sugens abounded in the majority of the pots. The pots were
then regularly emptied within a few days of each fall of rain. After four
weeks, when again allowed to remain for some time full of water, most of the
pots were free from larvæ. The few larvæ which were found, were those of
S. sugens.
In my own bungalow it was also possible, by attention to all small breeding-
places, to prevent mosquitoes being troublesome. A neglect of such precautions
was always followed by their presence in troublesome numbers. But although
the bungalow was in a very isolated position and its surroundings, including
the servants' quarters, readily examined, it was found impossible to quite do away
with mosquitoes, and stray specimens were constantly caught. On the whole, I
believe that operations against culex mosquitoes are followed by much more dis-
tinct results than those directed against anopheles. Both culex and stegomyiæ,
however, appear to find their way in small numbers to houses in spite of the
strictest care being taken to prevent them breeding in the neighbourhood.
19
III.—The effect upon malaria.
The aim of the experiments was in the first place the demonstration of a
reduction in malaria among troops. For many reasons, however, troops do not
form a very suitable community upon which to measure the effect of such opera-
tions. In the first place the figures of returns for malaria admissions are extremely
variable,* so that it is impossible to tell whether in any year a very small figure
is due to natural causes or to hygienic measures. From the following table
it will be seen how difficult it is to draw any conclusion from the yearly admission
rate as to the effect of the experiment in 1902. The figures for the Royal
Artillery were in that year certainly lower than in any previous year, but at the
same time the reduction in the number of admissions among the British Infantry
(untreated area) was even more marked :—
Year.
Strength.
Admissions.
Admissions per
thousand.
1898
All troops, 869
.
.
.
.
.
.
.
. 702
8 0 8
1899
,,
,, 853
.
.
.
.
.
.
.
. 400
469
1900
Royal Artillery, 259
814
.
.
.
.
.
.
132
878
509
1,079
British Infantry, 555
746
1,344
1901
Royal Artillery, 225 808 .
.
.
.
.
.
346
1094
1,538
1,354
748
1,283
British Infantry 583
1902
R o y a l A r t i l e r y ,
172
731
.
.
.
.
.
.
66
197
384
269
B r i t i s h I n f a n t r y ,
5 5 9
131
234
It also seems certain that the health of any given body of troops in any
particular year must depend not only upon the conditions then present in
the station (number of anopheles, infection, etc.), but also upon the state of
the regiment as regards the number of old infections, unseasoned men straight
from home, men from malarious stations, and so on. Moreover, not only are
statistics complicated by the movements of the men (as in the case of the
Delhi Manœuvres in 1902), but they are liable to depend very largely upon a
personal equation, since great differences exist in the degree of illness consi-
dered by different medical officers as necessitating admission to hospital. The
coming on duty, for instance, of a medical officer who admits even slight cases of
undoubted malaria, may double the admission rate for this disease. On the
other hand, slight cases may be only "detained," not admitted, and the admission
rate thus lowered.† On the whole, then, the number of admissions for malaria
among troops do not form the best test of the effect of operations.
* The figures for a number of years are given by Captain James in the first report, page 6.
† " Detained " cases are not shown in the official returns.
D 2
I have previously mentioned the presence in the area of several native
communities, viz. , the regimental bazaar, the syce lines and hospital followers'
lines. The people living in these, especially the children, form a much more
suitable community for testing the efficacy of the operations than the troops.
It is, however, obvious that if by mosquito destruction operations the
health of native communities is improved, the station is also rendered more
healthy for troops. In discussing the effect upon malaria we may therefore
notice : —
(a) Native malaria.—A comparison between malaria in the bazaars within
the area and malaria outside the area as evidenced by the endemic indices,
appeared to show that in spite of the poor results as regards adult anopheles, a
distinct effect was produced upon malaria. During August and September of the
present year the endemic index of both the Royal Artillery bazaar and the hospi-
tal followers' lines remained phenomenally low, being 0 and 4, respectively. The
spleen rate was however higher in proportion, being 36 per cent. and 41 per cent.
respectively. During the same months malaria in the British Infantry bazaar was
much as in other years, the spleen rate being 70 per cent. and the endemic index 30.
This highly satisfactory state of affairs was unfortunately not maintained through-
out the season, and it was found impossible to prevent the rate in the bazaars from
rising in October and November. In these two months the endemic indices in
bazaars in the area were high and apparently quite uninfluenced by the opera-
tions. We shall see later that all our results pointed to the same conclusion,
namely, that by the operations the onset of the fever season was postponed, but
that after the first two months no effect upon malaria was apparent.
Table showing spleen rates in bazaars within and outside the area of
operations :—
September.
October.
November.
Royal Artillery bazaar
(in area).
Spleen rate
.
.
36.6
6 4 . 5
64
Hospital followers lines
(in area).
Spleen rate
. .
41
6 0
6 0
Syce lines .
.
.
(in area).
Spleen rate
. .
45
67.5
54
British Infantry bazaar
(outside the area).
Spleen rate
.
.
70
77.5
77
21
(b) Malaria among troops.—An exactly parallel effect to that on malaria in
bazaars appeared to be produced upon the malaria of troops. Among the British
Infantry (who lived outside the area) men began to be admitted to hospital early
in August, the number of admissions for this month being 29 out of a total
strength of 477. In September malaria was still more prevalent, the admissions
being 92. Among the Royal Artillery, admissions were very infrequent in
August, being only 5 out of a strength of 240. In September the admissions
numbered only 19. So far then the difference between the two bodies of troops
was very striking. But later on malaria became much more frequent among the
men of the Royal Artillery, the admissions being 88 for October out of a strength
of 277, and 122 for November out of a strength of 285. The British Infantry were
at this time less affected with malaria, the admissions being 89 for October out of
a strength of 476, and 201 for November out of a strength of 723. In these
two months quinine was, however, administered under very strict supervision to
the British Infantry, and the lowered rate of admission might well be due to this
cause. The total numbers of admissions, from 1st July to the end of November,
were in the case of the British Infantry 416 and in the Royal Artillery 234, the
average monthly strengths being 448 and 264 respectively. These figures give
158 per mille per month as the admission rate for malarial fevers among the
British Infantry and 216 per mille per month as the admission rate for malarial
fevers among the Royal Artillery, the difference in the figures for the whole
season being therefore somewhat in favour of the British Infantry, who, as already
mentioned, lived outside the area of operations.
ADVOCATES LIBRARY
22
PART IV.
CERTAIN POINTS IN THE BIOLOGY OF MOSQUITOES NOTED DURING
THE ANTI-MALARIAL OPERATIONS.
T
HE species of anopheles found in Mian Mir have so far been
—
1 Anopheles Rossii (Giles).
[=Myzomyia Rossii. Theobald].
2
" culicifacies (Giles).
[=
,,
culicifacies.
Theobald].
3
" Stephensi (Theobald).
[= Nyssorhynchus Stephensi.
Theobald].
4
,,
fuliginosus (Giles).
[=
,,
fuliginosus.
Theobald].
5
,,
pulcherrimus (Theobald).
[= Cellia pulcherrima. Theobald].
6
,,
barbirostris (Van der Wulp). [=Myzorhynchus barbirostris.
Theobald.]
7
,,
minutus (Theobald).
[=
,,
minutus.
Theobald.]
It has already been mentioned that M. Rossii and M. culicifacies were the
common species and that the former bred in the rain-formed pools and the latter
in the canals and that, apart from such sources, these species were rarely found.
With regard to N. fuliginosus, it was noted that occasional adults occurred in the
bazaars and stables, but that the larvæ were only to be found in certain "grassy "
pools, of which there were about a dozen in the area. It was a curious fact
that though the larvæ of both M. Rossii and M. culicifacies were found in
these pools they occurred only in very small numbers. The only source of
N. fuliginosus was the outlying area, and in no case within 1,000 yards of the
situation where the adults were captured. This species is undoubtedly a com-
paratively " wild " species and breeds by choice in pools with much algae, lake
margins, etc. The occurrence of N. fuliginosus in such small numbers was the
more noticeable, since in the Central Provinces (Nagpur) and some other parts of
India where breeding-places of the above nature abounded, this species was very
numerous. The markedly wild species M. barbirostris were caught only in the
larval state and on the extreme limits of the area where water with much vegetation
occurred, and its adults were never seen in the bazaars. M. barbirostris —so
common in some parts of India—appeared unable to propagate itself in the
muddy pools and canals of Mian Mir. Adults of C. pulcherrima were caught in
small numbers all over the district, within and without the area. The larvæ of
N. Stephensi were mostly to be caught in " pots," but occurred also in stone
reservoirs, and sometimes in shallow and small pools.
23
The Culicidæ * other than anopheles found in Mian Mir were
—
Stegomyia fasciata.
,,
sugens (Wiedmann).
,,
scutellaris (Walker).
Culex fatigans (Wiedmann).
„ impellens (Wiedmann).
„ concolor (Desvoidy).
,, new species.
Tæniorhynchus tenax (Theobald).
,,
new species.
Melanoconion, new species.
Howardina, new species.
Mucidus scataphagoides.
Of these S. fasciata, S. sugens and C. fatigans were very common house-
hold mosquitoes and formed the bulk of the " culex " occurring in the bungalow
section. C. impellens and Melanoconion were extremely abundant species in the
outlying area, being found in almost all natural waters except the muddy rain
pools. Tœniorhynchus occurred in a few grassy and weedy waters. Adults
were caught mostly in the hospital followers' lines, half a mile from the nearest
known breeding-place (Groups E. and G. See map.)
The larvæ of both C. concolor and M. scataphagoides† are actively cannibal,
living entirely upon other larvæ. C. concolor was almost everywhere present in
pots, whereas the larva of mucidus was very common in natural waters. From
the frequency with which the larvæ of both species were found, the part played
by them in keeping down other species of mosquitoes must be considerable.
The most noticeable phenomena in regard to mosquitoes in the present
season were :—
1.—The swarming of certain species, both anopheles and culex, during
a comparatively short period, so that their numbers were quite
out of proportion to those found at other times.
Of all the species M. Rossii exhibited this " swarming" phenomenon in the
greatest degree. In July, larvæ of M. Rossii were practically never seen, the
only anopheles then found breeding being M. culicifacies, which was limited to
the canals. Even f or some time after the onset of the rains no larvæ were found in
the numerous pools then formed. By the third week after the first fall of rain, pools
containing larvæ (M. Rossii) were found more readily, and by the sixth week such
* Kindly identified by Mr. Theobald.
† See a later paper on the larval characters in relation to the classification of the Culicidæ.
24
pools were abundant. By the middle of September the larvæ of M. Rossii had
increased in numbers enormously and swarmed in the pools around the bazaars.
They were also to be found in the large majority of pools throughout the whole
country side, as well as in countless shallow puddles lying in the furrows of arable
land. At this time, no matter how far from habitations search was made, the
larvæ of M. Rossii were always readily found. By the end of September the
breeding places of this species had become much reduced, from the drying up of
the more shallow pools, and a few weeks later the breeding-places were localised
to a few spots where water still remained. The adult insects showed a corre-
sponding increase, and though before the rains found with the greatest difficulty,
they were to be caught in immense numbers in every bazaar and village in the
neighbourhood a few weeks later. They remained in large numbers in spite of
the reduction in breeding-places until the end of October, and then rather rapidly
disappeared.
Tables showing increase of M. Rossii in August and September. Observations
in British Infantry Bazaar.
LARVÆ.
Day after first shower of rain. Number of pools in imme-
diate neighbourhood.
Extent to which larvæ were present.
7
6
No larvæ found.
21
8
Abundant larvæ in one pool.
42
17
Larvæ abundant in 6 pools.
58
26
Larvæ present in every pool, swarming in many.
ADULTS.
Day after first shower of rain.
Number of adults in bazaar.
7
2 Specimens found after long search.
21
Adults very scanty.
42
Anopheles very abundant (M. Rossii).
58
M. Rossii "swarming."
9 8
Numbers of M. Rossii much reduced.
This increas e in the numbers of M. Rossii, from a species difficult to obtain
to one swarming in every situation, is undoubtedly due to the formation by the
rains of abundant breeding-places suitable for the species. The extremely small
n u mb e r o f l a r v æ o f t h i s s p e c i e s i n t h e f i r s t we e k o r t wo o f t h e r a i n s g o e s t o
show that at the end of the dry weather adults had almost disappeared. The
enormous increase during the later rains and ending when the rain pools have
25
become dry is then a very striking feature in the life history of M. Rossii. Such
a time of swarming is not confined to the Punjab, for in several parts of India
we have observed a similar phenomenon.
In July, larvæ of M. culicifacies were not abundant. Even uncleaned canals
contained very few whilst the cleaned ones were remarkably free from larvæ.
An increase, however, in the number of the larvæ in the canals began to be
noticed in August, and they increased steadily throughout September and
abounded in both cleaned and uncleaned canals in October. They then under-
went a striking diminution and almost disappeared with the onset of the cold
weather in November. The adults of M. culicifacies appeared to outlast those
of M. Rossii and captures of anopheles in the middle of November contained
more specimens of this species than of M. Rossii, a reversal of the conditions
prevailing earlier in the season when M. Rossii was caught far more readily than
M. culicifacies. In the case then of M. culicifacies there also occurred a very
marked increase at this time. The increase in M. culicifacies, however, could
not have depended upon an increased area of breeding-place, though the condi-
tions may have been rendered more favourable by a copious addition of rain
water to the canals. It is also worthy of note that the numbers of culicifa-
cies reached their maximum in October, whereas at this time M. Rossiiw a s
diminishing. On the whole the period of greatest prevalence of M. culicifa-
cies corresponded more closely with the highest incidence of malaria than did
that of M. Rossii. This is in keeping with what has been previously noted in
regard to the relation of these two species to malaria.
Rather late in the season N. fuliginosus and C. pulcherrima became more
common in the area and appeared to share in the general increase in
September and October. The occurrence of N. fuliginosus at this time was
peculiarly significant, since all grassy pools in which the larvæ were detected
had long been dried out. Specimens of this species must almost certainly have
flown in from beyond the limits of the area. *
Other Culicidœ. — Certain species of " culex " exhibited in a marked degree
the " swarming " phenomenon. A species of the genus Howardina occurred in
vast numbers during the period of heaviest rain. They appeared to occur in
single broods, one after each downpour of rain. Pupation appeared to occur in
all larvæ on the same day, and the extensive shallow pools in which they bred
lasted as a rule only sufficient time to allow the pupæ to hatch.
I I . — T h e f l i g h t o f a n o p h e l e s o v e r c o n s i d e r a b l e d i s t a n c e s .
A most important series of observations made on anopheles were those
relating to the distances they can fly. In every case the conclusion was that
* A l s o s e e t h e f i r s t r e p o r t o f t h e o p e r a t i o n s , p a g e 3 7 .
E
26
where an abundant food-supply existed anopheles travelled long distances (¾ of a
mile or more) to reach it, and that they traversed an equal distance if necessary
to lay their eggs. Where, however, a suitable breeding-place lay near at hand
they did not appear to pass it over. It has been already noted that the larvæ of
M. Rossii swarmed in pools immediately around bazaars, villages, etc. In the
height of the anopheles season such pools often contained so many larvæ that
they appeared, when looked at from a short distance, to be covered with a scum.
Around the edges of these pools also the ova were so abundant as to form a dis-
tinct black line. Such a state of affairs was, however, never seen under natural
conditions at any great distance from a large food-supply. But after all breeding-
places had been destroyed in the neighbourhood of the Royal Artillery bazaar by
the drainage or filling-in of all pools, larvæ were found in enormous numbers in
distant pools at T and M (see map). In order to determine exactly how far
anopheles will fly under these circumstances the above-mentioned pools were all
dried by baling out the water. The result of this measure was that larvæ then
swarmed in the pools of groups S, and N, where previously they had been present
only in small numbers. That the larvæ in these pools were derived from adult
M. Rossii coming from the bazaar was certain, and the flight of anopheles over
a distance of ¾ of a mile was therefore demonstrated.
Very abundant adult M. Rossii were found during August in the saddle
rooms in connection with the Royal Artillery stables. By this time all breeding-
places in the neighbourhood had been drained or filled up, and the pools at A, B,
and F, had been regularly controlled by oiling or baling out. Larvæ at this time
were swarming in the pools at C, though not in some pools still further away.
As adults continued to increase in the saddle rooms, they undoubtedly came
from the pools at C, the nearest pool being 900 yards distant.
We must then look upon the maximum distance to which anopheles ( M.
Rossii) will fly as not yet known. Under the conditions at Mian Mir, however, the
above experiments show that they fly to and fro a distance of at least half a mile.
In has been already remarked that adults of N. fuliginosus were not un-
common in the bazaars, stables, etc., and this in spite of the fact that larvæ of this
species only occurred on the extreme limits of the area. In the case of N. fuligi-
nosus there also appears to be a very considerable power of flight. With regard
to M. culicifacies it is also difficult to see where the adults came from in the
later part of the season unless distances of half a mile or more were traversed
by this species.
It is important, before leaving this subject, to briefly note what appear to be
the conditions influencing the flight of anopheles. That anopheles do not fly
long distances without good reason is most likely, and from many observations
it is our experience that the abundance of the food-supply is the factor deter-