498 THE POPULAR SCIENCE MONTHLY. 



do with the regulation of the body-temperature. If, by exposure to 

 cold, for example, heat is lost more rapidly from the surface than it is 

 supplied within, its warmth must decrease, and there needs but a 

 few degrees of fall to induce disease ; on the other hand, if, by ex- 

 posure to external heat, loss from the body is impeded, its tempera- 

 ture rises, and disease again results. 



In hot climates, or during the hot season in temperate latitudes, 

 we are in contact with an atmosphere which frequently attains a tem- 

 perature nearly or quite equal to that of the body ; and, at such times, 

 our sensations tell us that we are losing heat less easily than during 

 the cooler portions of the year. But, when thus exposed, the extensive 

 evaporating surfaces of the lungs and skin are called into more active 

 play ; and, if the air is of average dryness, heat is rapidly thrown 

 off by perspiration, the loss being so nicely adjusted that a uni- 

 form temperature of 99 Fahr. is continuously maintained. This heat- 

 regulating function of the organism is one of the marvels of physiol- 

 ogy. In spite of the vicissitudes of climate and season, it ever holds 

 the temperature at a uniform degree, and, even under the stress of high 

 artificial heat, is able to keep the balance comparatively unchanged. 

 Blagden and Fordyce exposed themselves in an oven to a heat of 

 260 Fahr., without serious inconvenience, and with but a slight rise 

 of temperature. But the air was dry, and the heat was kept down by 

 perspiration. The substitution of moist for dry air in the oven hin- 

 dered evaporation, and the temperature of the body rose rapidly. 

 With this hasty sketch of the heat-producing and heat-regulating 

 functions of the animal economy, we pass to a brief consideration of 

 some of the more important ill-effects resulting from the action of ex- 

 cessive heat on the conditions of health and on the body itself. 



High temperature is a powerful aid to decomposition. Dead or- 

 ganic matter, under its influence, speedily decays, giving rise to 

 foul and poisonous products which, escaping into the atmosphere, 

 find their way, sooner or later, into the system. Here they work 

 various forms of mischief. Like sulphuretted hydrogen gas, they 

 may be directly poisonous, or, like carbonic-acid gas, may act by 

 diluting the air, and so, by reducing the normal supply of oxygen, 

 interfere with the due oxygenation and purification of the blood. The 

 filth of towns is always highly charged with organic matter, and this, 

 when rapidly decomposing in the heats of summer, has long been recog- 

 nized as a prolific source of disease. 



Decaying vegetable matter in the soil is held to be the source of 

 malarial poison ; and here, again, if moisture is present, decay is al- 

 ways hastened and increased by excessive heat. So great, in the 

 opinion of Dr. Parkes, is the influence of heat on the development 

 and spread of malarious disease, that, in selecting a residence with a 

 view to escaping its effects, he recommends that, in tropical countries, 

 the point be 1,000 or 1,500 feet higher above the source of the poison 



