xxxviii Appendix, 



for days, and it may be that no time of year is more healthy. I am 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 arie 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. 



It 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. 



