THE MORBID EFFECTS OF HEAT. 499 



than is required in temperate latitudes. The remittent form of mala- 

 rious fevers, according to Dr. Maclean, " is most prevalent and fatal 

 where high temperatures and malaria act in combination." The same 

 authority also says : " I have, in a great many instances, observed in- 

 termittents pass at once into a severe type of the remittent form, ap- 

 parently from no other cause than the descent from comparatively 

 cool and elevated regions into the heated plains, and this under cir- 

 cumstances where there was no reason to believe that the sufferers 

 had been again exposed to malaria." 



In the production and spread of cholera, and yellow fever, exces- 

 sive heat also has an important share. Both are most intimately asso- 

 ciated with decomj)osing filth ; both are conveyable by the putrefying 

 stools of the sick, and both flourish most in hot climates and hot sea- 

 sons. In the case of cholera, the bad effects of extreme heat are abun- 

 dantly shown by what has been observed in the tropics. " In Ben- 

 gal," says Dr. Goodeve (Reynolds's " System of Medicine," vol. i., p. 

 129), " the hot seasons, including the hot, and dry, and rainy seasons, 

 have witnessed the worst epidemics." The most fatal cholera months, 

 in both tropical and temperate countries, are found between April 

 and September. Among European troops in Bombay, according to 

 Dr. Ewart's tables, which cover a period of eight years, more than 

 50 per cent, of the cases treated in the six months from April to 

 September died, while but little over 19 per cent, of the cases treated 

 in the other six months of the year were fatal. That the disease oc- 

 curs in winter is undoubted, but that it is much less general and severe 

 is equally true. Yellow fever, though resembling cholera in many 

 ways, is unlike it in this a temperature of 70 or 72 Fahr. is abso- 

 lutely requisite to its development and propagation, and the occur- 

 rence of frost at once puts an end to its ravages. 



Heat also contributes largely toward the production of diarrhoea, 

 its more common form, in recognition of this, taking the name of 

 summer complaint. The disease is far more common and more fatal 

 in hot than in cold climates, and in the summer season of temperate 

 climates than in the winter. Putrefying organic matter, held in sus- 

 pension in drinking-water, is, according to Dr. Parkes, one of the most 

 common causes of diarrhoea, and this condition of the water is very 

 frequent in summer, and comparatively rare in winter. 



In all these instances heat appears to act not so much upon the 

 body itself as upon the various external agencies influencing health. 

 It is to bad conditions what fire is to powder. If the match is with- 

 held, the powder is harmless ; but, as the two are liable to come 

 together, we secure safety by removing the magazine. So the pres- 

 ence of filth in water, in soil, and above-ground, may be innocu- 

 ous by itself, but let the action of heat touch it off into decompo- 

 sition, and we at once get the effects in the shape of disease. Heat 

 thus aids the pollution of both air and water, keeps alive and active 



