250 Prof. Hosking on Ventilation. 
influenced by the circumstances under which the process may be 
carried on. Whether it’be on the hill-side, open to the winds of 
heaven, or in a close room, from which all draught of air is ex- 
cluded, the expired breath, as it leaves the nostrils heated. by the 
fire' in the lungs, rises, or seeks to rise, above their level, and may 
not be again inhaled. Out of doors the cooler or less heated air 
of the lower level presents itself for respiration unaffected by the 
spent exhaled air, but in a close apartment, the whole body of 
included air must soon be affected by whatever process any por- 
tion of it may have undergone. The process by which nature 
carries off spent air, purifies, and returns it uncontaminated, is 
thus checked by the cireumstances under which we place our- 
selves within doors. All our devices for shelter from the weather, 
of the fire less easily than the lower air, or that at and about the 
level of the fire; and the lower air, or air at the lower levels, 
forces its way in, therefore, by any opening it can find or make 
—through the joints of the flooring-boards, and under the skitt- 
ans i 
sought of obtaining heat without the offending fire. Ventilation 
is not thought of yet. ee 
