180 EFFECT OF ANNUAL VARIATIONS OF HEAT. 



mid-summer and their minimum soon after mid- winter, the manner in 

 which the system comports itself under them, and the means which in- 

 stinct and experience teach us to employ in providing against them. 



The tables of mortality show that there is a loss of life at the annual 

 imu rnax i mum an d minimum of temperature which greatly ex- 

 ai variations ceeds the average of any other period. In England and Bel- 

 gium, where the mean temperature of the summer months is 

 moderate, this is not so strikingly marked for those months, and the chief 

 loss falls upon the winter ; but in New York, which has a summer cor- 

 responding to that of the south of Europe and a winter like that of the 

 north, the effect of these extremes becomes so obvious as even to be 

 popularly connected with the position of the thermometer above or below 

 55. Among infants and the aged, whose controlling powers over tem- 

 perature are imperfect, these effects are most distinctly witnessed ; but 

 among healthy adults, and even in Europe, we can detect them on crit- 

 ical examination. Thus, in Brussels, the monthly mortality for January 

 being taken as 105, that for July is 91, for August 96, and for October 

 93 ; and it is to be recollected that these are the residual traces of the 

 operation of cold and heat after all the precautions have been used to 

 ward them off. I might make here the same remark that was made 

 when considering diurnal variations, that the true effect is so masked and 

 concealed that we are liable to undervalue it, and do not properly appre- 

 ciate this tax put upon the system. 



These annual variations of external temperature are chiefly combated 

 Control over ty food, clothing, and shelter. The dietetic changes we make 

 annual varia- between winter and summer are founded upon the principle 



tions by food, - ' . , .-ri ./ - i - 1* j -11 



clothing, shel- of using more combustible food for the former, and less com- 

 bustible for the latter season ; and, since the calorific ef- 

 fect of an article of food greatly depends on the quantity of oxidizable 

 hydrogen it contains, the winter diet has more of that element than the 

 .summer. Partly thus by varying the nature, and partly by varying the 

 quantity of the food, we can effect a compensation to a certain extent. 



Of the manner in which the diet-compensation is aided by variations 

 in clothing little needs to be said. The experiments of Count Eumford 

 established the fact that the conductibility of summer clothing is greater 

 than that of winter, and therefore its resistance to the escape of heat is 

 less. It is sufficient merely to allude to the control which is gained by 

 difference of thickness in the garments, and by their amount or quan- 

 tity. We instinctively make these adjustments to meet the existing ex- 

 igencies, and, as far as may be, in this manner aim at a medium effect. 



The check upon external temperature by the use of clothing was doubt- 

 less one of the first contrivances of the human race. Even of savage life 

 it is a cardinal feature. The check by adjustment of diet belongs to a 



