630 
VENTILATION. 
Lastly. Iii the moisture so exhaled from the body there 
is a quantity of excreted animal matter disengaged from the 
system, which, were it retained, would be fatal to health 
and life. 
The expired air, therefore, is found to differ very much in 
composition. It is stated to have lost from 4 to 6 
per cent, of its oxygen, and to have acquired from 3*5 to 5 
per cent, of carbonic acid gas in combination with ammonia 
and a large proportion of aqueous vapour, whilst the 
proportion of nitrogen varies but little, the quantity lost 
being very inconsiderable. 
The quantity of air which passes through the lungs of 
man during ordinary respiration has been variously esti¬ 
mated, about twenty cubic inches being considered as the 
correct quantity. 
But of this the lungs cannot be completely emptied even 
by the most violent muscular effort. The residual air has 
been calculated at from 40 to 260 cubic inches. 
Philosophers of all times and of all nations have earnestly 
endeavoured to solve the problem of how much oxygen is 
consumed, and how much carbonic acid gas is given off, 
during the process of respiration. The results of their experi¬ 
ments are as varied as the attempts have been numerous. 
Dr. Pickford, in his excellent work, # says—“ Assuming that 
a healthy adult male respires twenty times in a minute, and 
takes into his lungs, at each inspiration, 20 cubic inches of 
air, he would inspire 400 cubic inches in a minute, 24,000 
in an hour, or 576,000 in twenty-four hours.” 
Assuming, also, that the expired air contains 4 per cent, 
only of carbonic acid, he would evolve 16 cubic inches per 
minute, 960 per hour, 23,040 in the twenty-four hours == 
3*529 grains, or 7 ounces 2 drachms 49 grains, of carbon. 
Scharling who, has also recently investigated the subject, 
states that a powerful adult man exhales, in the course of 
twenty-four hours about 30*6 ounces of carbonic acid, which 
corresponds to 8*34 ounces of carbon. 
If these calculations are correct, it follows that the horse 
(having live times the capacity of man) takes into his chest 
at each inspiration 100 cubic inches of air; allowing eight 
respirations per minute, he would inspire 800 cubic inches 
per minute, or 48,000 cubic inches in an hour; and if the 
expired air contains only 4 per cent, of carbonic acid (which 
is a low standard), 4800 cubic inches of that gas will have 
been produced in this space of time. 
Faraday has somewhere stated that an adult human being 
* Pickford, Dr., on ‘ Hygiene/ 
