Sioux City Academy of Science and Letters. 55 
There is one other point, among many, which I feel 
impelled to mention in this consideration of ventilation, 
and that is in regard to the proper degree of humidity 
which is desirable in the atmosphere of our school rooms. 
Our school rooms, during the part of the year when artifi- 
cial heat is necessary, are kept by regulation of a temper- 
ature of from 65 to 70 degrees F., but without any care 
as to the amount of moisture the air contains. Now, if a 
given volume of air be taken from without at a tempera- 
ture of 30° F. and a humidity of 80 per cent., for 
instance, and heated to 68° F., it will contain per 
given volume only 202 per cent. of moisture. In other 
words its relative humidity has been decreased from 80° 
to 20° through heating and expansion and its con- 
sequent increased capacity to hold moisture. If 
air, therefore, when heated, is not supplied with a 
proper amount of moisture, it takes up moisture from 
every object that will yield it. The effect on things about 
us is very evident to ordinary observation, but the effect 
of dry air upon the bodies of persons who are subjected 
to it is not so clearly observable. Nevertheless it is just 
as positive. The artificially heated air, in which but a 
small per cent. of moisture remains, absorbs moisture 
from the skin, the lining membrane of the nasal pas- 
sages, the mouth, the throat, and the lungs. 
In an examination, a few years ago, of a very ex- 
pensive heating and ventilating apparatus that had been 
placed in a grammar school, Prof. Shaw of the Institute 
of Pedagogy of New York University, found the humidity 
of the air at 10.15 a. m., to be 25 per cent. There were 
700 pupils in the building. These pupils passed through 
an air of 80 degrees humidity in going to school, breathed 
an air of 25 degrees humidity from 9:00 o’clock ’till noon 
when they were sent out into an atmosphere having 80 
per cent. humidity. They returned in the afternoon to 
breathe the same dry air and to be dismissed again into 
a more humid atmosphere. Such changes as these, the 
pupils of many schools undergo repeatedly in the winter 
season. Such conditions are unquestionably a cause of 
colds and inflammation of the throat and bronchial pas- 
sages. Could the real effects of these imperfect condi- 
tions in our school rooms be fully realized by the public, 
