190 
POPULAE SCIENCE EEVIEW. 
he is attacked with diarrhoea. It is from this extent of action 
that the mortality of all diseases runs np so fast^ when the low 
wave of heat rolls over the population^ takings as we have 
seen^ the feeblest first. 
Another danger sometimes follows which is remote,, but may 
be fatal^ even to persons who are in health. It is one of the 
best known facts in science that when a part of the outer surface 
of the body has been exposed long to cold^ the greatest risk is 
run in trying suddenly to warm it. The vessels become 
rapidly dilated,, their coats give way^ and extreme congestion 
follows. But what is true of the skin is true equally, and with 
more practical force, of the lungs. A man, a little below par, 
goes out when the wave of temperature is low, and feels 
oppressed, cold, weak, and miserable ; the circulation through 
his lungs has been suppressed, and he is not oxidizing : he 
returns to a warm place, he rushes to the fii’e, breathes eagerly 
and long the heated air, and adds perchance to the warmth by 
taking a cup of hot drink; then he goes to bed and wakes 
in a few hours with what is called pneumonia, or with bron- 
chitis, or with both diseases. What has happened ? The 
simple physical fact of reaction under too sudden an exposure 
to heat after exposure to cold. The capillaries of the lungs 
have become engorged, and the circulation static, so that there 
must be reaction of heat, — inflammation, — before recovery can 
occur. Nearly all bronchial affections are induced in this 
manner, not always or necessarily in the acute form, but more 
frequently by slow degrees, by repetition and repetition of the 
evil. Common colds are taken in this same way : the exposed 
mucous surfaces of the nose and throat are subjected to a chill ; 
then they are subjected to heat ; then there is congestion, 
reaction of heat, pouring out of fiuid matter, and all the other 
local phenomena. 
The wave of low temperatm’e rolling over a given population 
finds inevitably a certain number of persons of all ages and 
conditions on whom to exert its power. -It catches them too 
often when they least expect it. An aged man, with sluggish 
heart, goes to bed and reclines to sleep in a temperature say of 
60° or 55°. In his sleep, were it quite uninfluenced from 
without, his heart and his breathing would naturally decline. 
Grradually, as the night advances, the low wave of heat steals 
over the sleeper, and the air he was breathing at 55° falls and 
falls to 40°, or it may be to 35° or 30°. What may naturally 
follow less than a deeper sleep ? Is it not natural that the 
sleep so profound shall stop the labouring heart ? Certainly. 
The great narcotic never travels without fastening on some vic- 
tims in this wise, removing them, imperceptibly to themselves, 
into absolute rest, inertia, until life recommences out of death. 
