626 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
(to vary the condition of ozonization of the air) must have samewhat 
influenced our results by altering the cooling effect of the air on the 
body. These tests were carried out in warm summer weather, and 
in the final experiment the windows were kept shut all the time and 
the room ventilated by opening the doors leading into other and 
larger laboratories. In this experiment we obtained results which 
we regard as the most conclusive of all. 
The metabolism varies with the degree of complete rest of the 
subject. If he moves slightly more or less—e. g., in reading, talking— 
this will affect the result, and thus we can not expect figures more 
concordant than those we have obtained. Looking at the figures in 
columns 4 and 6, we can not find any conclusive evidence that ozone 
altered the respiratory metabolism. Note particularly the final 
experiment (No. 7), in which the windows were shut and the con- 
ditions even all through. 
The ozone was given in a concentration that made the air smell 
quite strongly, and in some cases it was pushed even to an unpleasant 
degree. Taking these figures together with those obtained on mice, 
we must conclude that we have failed to obtain certain evidence that 
inhalation of ozone in weak concentration stimulates the respiratory 
metabolism, 1. e., the output of CO, and use of O,. On the other 
hand, our experiments conclusively show that any considerable con- 
centration of ozone depresses the respiratory metabolism. 
We think that the beneficial results obtained by the use of pure 
ozone in ventilation must be reached by the effect of ozone on the 
nervous system—by its stimulating the mucous membrane, neutraliz- 
ing smells, and relieving the depressing uniformity of close air. Our 
experiments show that no harm results to man from breathing air 
ozonized till the air smells quite strongly of ozone, for periods of 
half to one hour. 
Perhaps the most interesting observation made in the research is 
this: When the respiratory tract is irritated by ozone the animal 
becomes motionless, sits hunched up with its fur erect, thus showing 
the signs of depression. The ozone lessens the respiratory exchange, 
reduces it even to one-seventh, at a time when the lung shows no 
changes visible to the naked eye; the animal adjusts its behavior to 
this condition, and keeps very still and quiet. Its body temperature 
at the same time falls. The damage to the lung can not be serious, 
since this depressant effect is quite evanescent. 
