460 POPULAR BOTANY. 
and sustained, the same effects also a very important alteration in our 
blood. When the air, consisting, as we all know, of about sixty-six per 
cent, nitrogen gas, and thirty-three per cent, oxygen gas — comes in con- 
nection with the so-called chyle in our lungs, both of them (namely, the 
air and chyle) undergo thereby a strange alteration. The white chyle 
deprives the air of a part of its oxygen, changes thereby its white colour 
into e red, and is thereafter real blood, which is then pumped by the 
pulsation of the heart through the veins of the whole body, for the 
purpose of developing and nourishing the same to the remotest ex- 
tremitiep. 
As equivalent for the oxygen received, the chyle, however, delivers 
to the oxygen of the atmosphere a part of the superfluous carbon, pro- 
ducing thereby carbonic acid gas, which after this process is exhaled in 
company with the unchanged atmospheric air, nitrogen gas, and some 
moisture, which will intermix with the atmosphere. 
Beside by exhalation, carbonic acid gas is produced by the process of 
burning, of fermentation, putrefaction, by volcanic eruptions, by escap- 
ing from natural mineral springs, and many others. If we now consider 
how many millions of human beings and animals have already lived and 
breathed since the Creation ; how much combustion has taken place, and 
how many substances, both vegetable and animal, have gone to decay, 
&c. ; and if we consider further more, that by all these occurrences oxygen 
is constantly absorbed from the air and carbonic acid gas produced in 
return, one would fear that after the lapse of time the oxygen 
would decrease, while the carbonic acid gas would increase in such pro- 
portions that animal life could no longer be possible. 
The learned men of the olden times entertained this idea, hinting 
frequently at this danger, and as the effect of the carbonic acid gas is 
suffocating, when exceeding the proportion of four per cent, in the at- 
mospheric air, they feared the time would arrive when animal life on 
our globe would entirely cease to exist. Most happily for us, however, 
as well as for our descendants, the apprehensions of the old naturalists 
have proved to be unfounded ; for since the science of analytical che- 
mistry has attained so high a degree of perfection that its results may be 
considered scrupulously correct, the atmospherical air has frequently been 
analysed at regular intervals and in very different places and localities, 
the result always demonstrates that the proportion of the carbonic acid 
gas to that of the atmosphere is nearly constant, and in no place what- 
ever exceeds one per cent. 
For a long period the scientific world had speculated as to what be- 
came of the carbonic acid gas thus produced, nntil finally the German 
chemist, Liebig, proved, by facts, that the plants dissolve and decom- 
pose the carbonic acid gas of the atmosphere by absorbing its carbon 
for the formation of their growth by leaving the oxygen to escape as gas, 
which, by again dissolving into the air, begins its work anew. By this 
