2l6 
Relation of Moisture in Air 
[April, 
minimums of cold are reached, and at zero the production 
of a summer air in a house or place of residence may be 
claimed to be impossible. If the effect of the changes of 
out-of-door temperatures and humidities, which can happen 
with, at the worst, eight to twelve hours of change, and 
which on the average gives twenty-four to seventy-two 
hours of interval, is as objectionable, what words can ex- 
press the effeCt of the mere passing from a room at summer 
humid warmth to the open anhydrous air at zero ? There 
are few readers of this paper who have not tried the expe- 
riment of leaving some crowded hall, where the closed doors 
and windows and many breaths had made an approach to 
the summer condition, and felt the cold air of winter at the 
bottom of the lungs, as the inactive membrane parted with 
its unexpected supply of moisture to the anhydrous air. At 
whatever temperature or moisture condition air be inhaled, 
it will be exhaled at 90°, and laden with moisture nearly to 
the point of saturation. Of the heat given out by the 
lungs, that which proceeds from evaporation is generally 
largely in excess of what is required to impart heat to the 
air. Even in the extreme case of breathing air at — 40° (or 
the temperature when mercury freezes, which the writer 
once observed at Vassalborough, Maine), the heat of evapo- 
ration of moisture from the lungs is but a little greater 
than that for heating the air, being 2*22 units in one case 
to 2*18 units in the other, per cubic foot of exhaled air. 
The skin gives out its heat through insensible perspiration, 
or through heat imparted to air in similar, if not the same, 
proportion. 
The establishment of a regime of evaporation from the lungs 
or skin— of a constancy of secretions- — appears to be more essential 
than the establishment of a uniform temperature , either of the air of 
respiration or of contact with the person. The stability of the 
moisture condition, whether in the external air from time to 
time, or between inside and outside of the room, is what is 
desirable for health ; and this stability, from inside to out- 
side of room, is what we must maintain if we are to live in 
aCtive, healthful life in our climate. The transfer of heat 
through the skin or membranes is merely conductive, not 
involving organic aCtion ; while the supply of moisture 
incident to the maintaining of evaporation brings into 
service vessels, duCts, or pores, whose healthful aCtion de- 
pends in great measure on the regularity and continuity of 
the said service. This hypothesis will explain at once the 
healthfulness of the climate of Florida or that of Minnesota 
in cases of pulmonary disease, and in other parts of the 
