1819.) t and on the Blood in general. 269 
on the data of Messrs. Allan and Pepys, which are supposed to 
be the most accurate, will elicit from his lungs upwards of 11 oz. 
of carbon. The quantity of water discharged from the lungs 
during the same time has been estimated at about 20 0z.* With 
respect to the inferior animals, I am aware of no experiments 
made upon different individuals of the same class that we 
can compare with one another. 
Fourthly, We have to consider whether the phenomena of 
respiration be liable to any differences in degree in the same 
individual at different times; and to this part of our subject no 
one, except Dr. Fyfe and myself, seems to have much attended. 
Our experiments, however, have led us both to the same conclu- 
sion; namely, that the quantity of carbonic acid gas found in 
the lungs is liable to be very materially affected in its quantity in 
the same individual by various circumstances. These variations 
in quantity may be considered as of two descriptions, viz. general 
or diurnal variations, and particular variations. With respect to 
the first, all my experiments have tended to show, that the 
quantity of carbonic acid gas formed by the lungs is greater 
during the day than the night, and that the quantity begins to 
increase about day-break, and continues to do so till about noon, 
and afterwards decreases till sun-set. During the night it seems 
to remain uniformly at a minimum. The maximum quantity 
given off at noon, I have generally found to exceed the minimum 
by about one-fifth of the whole. Different days, however, 
differed in all these respects ; and from causes of which I am at 
, present entirely ignorant. Mr. Brande states, that he has found 
the quantity given off to be greater towards night,+ but I have 
not observed this. As to particular variations, it appears that 
there are many more circumstances which have a tendency to 
diminish the quantity than to increase it; and that wherever it 
has been inordinately raised or depressed, either above or below 
the standard, it is subsequently, in a certain degree, depressed or 
raised above the standard, thus preserving upon the whole a 
constant mean quantity. The passions of the mind appear to 
have a great influence over the quantity ; those of a depressing 
kind, diminishing it, and those of the Opposite nature, the 
reverse. Exercise, when moderate, appears to increase in some 
degree the quantity; but violent and long continued exercise 
diminishes it. The greatest decrease experienced was from the 
use of alcohol and vinous liquors in general, especially when 
taken upon an empty stomach. In short, whatever diminishes 
the powers of life, as low diet, mercurial irritation, &ec. appear 
both from Dr. Fyfe’s experiments as well as my own, to have 
the effect of diminishing the quantity. The quantity is also 
apparently much diminished during sleep. Some are of opinion 
that there is more carbonic acid given off a few hours after eat- 
* Berzelius’s View of Animal Chemistry, p. 39, 
+ Phil. Trans, 1809, Nicholson’s Journal, vol, xxv. 
