140 
AXXIVERSARY ADDRESS 
powers, conveying the food we eat to every part of the frame ; and 
(b) by virtue of its fluidity, maintaining the otherwise solid and 
rigid tissues of our system in that elastic and pliable condition 
essential to life and to activity. Nature demands that water, and 
water alone, shall fulfil these functions; the fulfilment being 
governed by exact chemical and physical laws. 
THE AIR WE BREATHE. 
A whole series of beautiful natural laws, those which we term 
chemical and physical laws, regulate the composition of the air 
we breathe, and regulate its temperature, pressure, purity, and its 
other properties on which, in a greater or less degree, the main¬ 
tenance of health depends. The burning within us of the fuel-like 
portion of our food, already mentioned as maintaining our warmth, 
is accomplished by the air inspired by our lungs under laws more 
especially studied by the chemist. The poisonous product of that 
combustion, expired from the lungs, passes away into the air from 
the region of the mouth and nostrils, under the laws, chiefly of 
heat and of diffusion, more especially studied by the physicist—as 
explained in the previous anniversary address. Again, between 
the pure air and food we take in on the one hand, and the used-up 
air and other products we give out on the other hand, there are 
formed within us numbers of compounds under laws more especially 
studied by the physiologist. The meteorologist takes note of the 
effects of those physical laws which govern the pressure, tempera¬ 
ture, and moisture of the air; effects which so much influence the 
comfort and the health generally of man. The study of each and 
all of these laws relating to the air we breathe is of unbounded 
interest, and would afford pure and unending pleasure to any 
student; but especially would the study charm and delight the 
student investigating them for purposes of mental recreation. At 
the same time, the breathing of air is so much less under our 
control than the eating of food or the drinking of fluids, that the 
majority of persons cannot be expected to find that interest in the 
study which it is capable of yielding. We are connoisseurs in 
the matter of eating and drinking, or we think we are ; while we 
take the air pretty much as it comes, having in fact no choice in 
the matter. We do something in cold weather towards warming 
and a little towards changing the air of inhabited rooms, subjects 
that will be noticed in connection with that of the dwellings we 
occupy; and the inhabitants of large towns have done something, 
though not so much as might be done, towards diminishing the 
volumes of grosser impurities discharged into the air from chimneys, 
