F. C.
MINETT
93
On the other hand, the change may be intrinsic
in origin and connected with seasonal modifica-
tions in endocrinal activity.
Apart from the two factors named above, a dry
hot atmosphere will promote dust formation, es-
pecially when there is some movement of the air,
and this by irritating the mucous membranes may
assist the penetration of infective material. Rain-
fall and moist atmospheric conditions will have an
opposite effect. Incidentally, it may be mentioned
that, contrary to what is sometimes imagined,
haemolytic streptococci are not delicate organisms.
Thus, it has been shown that they can survive in
dust for weeks and are often abundant in the air of
rooms that have been occupied by human beings
suffering from streptococcus disease [White, 1936 ;
Brown and Allison, 1937].
By way of comment on these predisposing caus-
es, it may be said that some drying effect on the
respiratory tract of young horses may occur at
certain seasons, e.g., in May and June at Mont-
gomery, and this adverse effect may be enhanced
by an excess of dust in the atmosphere. This,
however, is little more than a guess, and the data
at hand scarcely permit a serious consideration of
the possibility. Again, as to whether there is any
transient variation in the animals' resistance,
little can be said. If there is, it can hardly be due,
in this case, to lack of green food. Of the causes
mentioned, the influence of chilling must
be regarded as of preponderating importance,
especially in young animals, and the evidence
produced in this paper supports the statements of
observers on the spot. The lack of adequate
shelter under winter conditions in the Punjab must
put a severe strain on the animal's heat regulation,
and it is strongly felt that insufficient attention has
been paid to means for remedying this. (The
photographs accompanying my previous paper are
believed to provide evidence of this.)
The Climatological Atlas of India shows that the ab-
solute minimum temperature in December and January
(the coldest months) is around 28°F. at Khushab (Shahpur
District), slightly higher at Montgomery but still very low
viz., 30°F., while at Ahmednagar it is 40° to 45°F. Mean
minimum temperatures for these months are about 40° to
41°F. at Khushab, 42.5° F. at Montgomery and 53°F.
at Ahmednagar (see also Table I).
It has been pointed out above that the winter
storms of the Punjab and the northerly breeze at
this season in the north-west of the province will
reinforce the action of cold, but that the more
southerly breezes at the time of the summer rains
are unlikely to have much damaging affect. It
seems likely also that the reason why donkeys
usually escape the disease is simply because they
have much heavier coats, and not because they are
inherently more resistant. Objections to shelters
have been raised on the score of cost but all that is
really needed are cheap constructions. In the day
time, simple mud-brick walls would suffice to keep
off driving wind and rain or a mud-wall enclosure
might be provided in each paddock as refuge both
by day and night in bad weather. The planting
of trees as wind-breaks may also be recommended.
It may thus be said that there seem to be two
important factors involved in the epizootiology of
strangles, (a) the cold and rain of the Punjab
winter, which, perhaps by increasing a normally
elevated carrier rate at this season, is largely
instrumental in initiating outbreaks and thereby
augmenting the dosage of infective matter in the
locality; (b) at the depots the introduction of
fresh susceptible young stock at a particularly
dangerous time, viz. late in the purchasing season.
As Allen [1923] says, ' It is impossible to control
strangles if
young stock are received
as late as April or May when strangles is usually
at its height'. This second factor, however, may
be misleading and cause one to overlook the
point that the initial stimulus has been unfavour-
able weather conditions. The relative importance
of these two factors will no doubt vary to some
extent in different years, and it is unnecessary to
hold rigid views. But it is difficult to escape the
conclusion that, from the meteorological point of
view, the remount depots and horse-breeding
farms of the Punjab are unhappily situated.
SUMMARY
Equine strangles, as studied in India, is chiefly
a disease of the colder months. In this respect it
resembles certain respiratory diseases of man, e.g.
scarlet fever, colds, and pneumonia. Thus, it has
been shown that in the Punjab the attack rate is
significantly higher in the cold season than in the
hot and is significantly lower in the summer rainy
season. At Ahmednagar (Bombay), where the
climate is more equable than in the Punjab, the
attack rate also rises significantly during the drier
and cooler months and falls during the warmer wet
months from April to October.
Further support to the general conclusion is
derived from an examination of local meteorologi-
cal data which in the Punjab show some degree of
association between low absolute minimum tem-
peratures and the onset of outbreaks.
The association between weather conditions and
strangles is studied to best advantage at the farms
where the stock are reared ; at the depots, condi-
tions are somewhat artificial and the observations
are confused by the fact that the numbers of
susceptible stock are mounting fairly rapidly
throughout the winter, while by May outbreaks
tend to terminate abruptly owing to the shortage
of susceptibles. In general, the observations are
complicated by the facts that, while outbreaks tend
to develop in the cold weather, they may continue