1878.] 
to Health and Comfort. 
197 
§. Comfort, if not existence, depends upon a constant loss 
of heat from the person. The internal natural warmth of 
the body is very nearly ioo° F., regardless of the heat of the 
external air ; and the personal comfort which proceeds from 
the temperature and humid condition of the air, proceeds 
from the cooling effeCt which must then occur with constancy 
and regularity, and yet not so fast as to produce the sensation 
of cold. The origin of the natural heat is well established. 
There is inhaled by each adult in comparatively still life, 
each three to four seconds, from 30 to 40 cubic inches of air, 
at such temperature as may exist at the place, with extreme 
differences of temperature ranging from — 40° to +140° F., 
and with extremely variable proportions of humidity, from 
the point of saturation on the one hand to that of nearly an 
anhydrous air on the other. The practical extremes in our 
country are from little below zero to about ioo°, accompanied 
also with great variation of humid condition. A portion of 
the oxygen of the inhaled air is consumed in the system, and 
the exhalation, which follows each inhalation, emits about 
4 per cent of carbonic acid and iT per cent of vapour of 
water. Two or three grains of carbon are consumed in the 
system each minute, giving out 3! to 5J units of heat, the 
unit of heat being the equivalent to a pound of water heated 
i° F. It is the dispersion of this heat which establishes the 
sensation of comfort. Modern theory has established the 
convertibility of heat to work or power, and some portion of 
the heat evolved by the air of respiration will have been con- 
verted into labour or effort, but far the greatest portion will 
have been utilised in preserving the temperature of the body 
from the losses by evaporation of moisture, by conduction, 
and by radiation. One portion of the loss is readily esti- 
mated. The breath is inhaled at whatever temperature and 
humidity may subsist at the place, but is exhaled at all 
times at 90° (when the temperature of the air is not above 
that degree), and it is saturated with moisture at that tem- 
perature. If it is supposed that the temperature of the 
external air is 6z°, and the dew-point 54° (== 65 per cent 
humidity), from 0*35 to 0*56 unit of heat will have been ex- 
pended in evaporation of moisture in the lungs and throat, 
and o*io to 0*17 unit of heat in imparting heat to the exhaled 
air each minute. About three and a half times as much heat 
will have been expended in supplying the moisture as in 
heating the air. The loss of other portions of heat cannot 
be as definitely estimated. It is evident that it must mainly 
be dispersed from the skin, and it is pretty certain that a 
large, if not much the larger, portion must pass off in 
