xxxviii Appendix. 
for days, and it may be that no time of year is more healthy. Iam quite 
aware that intense cold does produce very dangerous attacks of capillary 
bronchitis, especially in old people, but I do not think that many bronchitic 
attacks among infants are thus originated. The epidemics of influenza and 
bronchitis, to which such attacks are generally due, that occur so frequently 
during the winter and spring months, seem to be produced by some other 
agency than the cold itself. Sudden changes of temperature in themselves are 
scarcely sufficient to bring about such results. There seems to be some other 
factor at work in these catarrhal disorders that are at times epidemic over 
such a large area of country. They may be due to some peculiar state of 
electrical tension in the atmosphere, that is produced at times in cold weather, 
or rather during sudden changes of temperature ; or they may be allied to 
those zymotic disorders that seem to be dependant on the influence of some 
germs of which we know little, either as to their mode of production or 
their character, but I think we may safely come to the conclusion that cold 
itself is not by any means a chief factor in their production. 
But a careful consideration of the circumstances under which intestinal 
disorders are most prevalent, leads to the conclusion that high temperature, or 
rather continued high temperature, is one of the most important factors at 
work. It seems to act, if I may use the expression, in a cumulative manner. 
The high mortality takes place only after a certain quantum of heat has been 
allowed to expend its influence. Suddenly occurring high temperature, which 
lasts only for a short time, is not followed by these pernicious effects. The 
high temperature seems to act in the first place as a predisposing, and in the 
second place as an exciting cause. After the system has been weakened by 
continued exposure to excessive heat, a further exposure is found to produce 
these intestinal affections, 
> TIt is on this account that in the summer of 1870-71, which was 
comparatively cool, the chief mortality was at the end of the summer, even 
with a declining average temperature for the month of March in which it 
occurred ; but in the summer of 1871-72, after a hot November and 
December, the sudden high increase of temperature in January is accompanied 
by a sudden and great increase in mortality, The gradual decrease in the 
mortality after that date is in accordance with the laws that are found to 
obtain in all epidemics, a certain number of those exposed to any morbid 
influence, on account of some previous constitutional state are especially 
susceptible, and are first and chiefly affected, and the rest suffer in a minor 
` degree. Thus the continuation of the high temperature in February and 
March, 1872, might. produce a less result than a lower temperature in 
February and March, 1871, because those most susceptible to the morbid 
influence of heat had been already attacked in January of that year. 
