I o 
The Colorado Experiment Station. 
of protein. In fact, carbon enters into the composition of prac¬ 
tically all plant and animal tissues. From this, it is clear that the 
demand for carbon must be very great, and in order to satisfy the 
demand, either the supply must be unlimited or the carbon is used 
over, and over again. We shall find that the latter is the case. As 
pointed out elsewhere, plants obtain this element from the carbon 
dioxide of the air, of which about three parts in ten thousand are 
carbon dioxxle. Animals secure their carbon from their foodstuffs, 
most of which come either directly or indirectly from plants. In 
the last analysis, it is plain to be seen that all of the carbon dioxide 
comes from the air. The supply of this gas is maintained practic¬ 
ally constant in Nature through the oxidation of carbon and its 
compounds. Immense quantities of carbon dioxide are returned 
to the atmosphere during the burning of coal, wood, and gas. The 
carbon in these substances unites with oxygen to form carbon diox¬ 
ide, the hydrogen combines with more oxygen to form water, and 
the mineral residue constitutes the ash. Many organic substances 
are eaten by animals, and, after serving their purpose, the carbon 
which enters into their composition is exhaled as carbon dioxide. 
Another very important agency in setting free carbon dioxide 
is the work of micro-organisms. It was believed for a long time 
that the splitting up of complex substances during decay, accom¬ 
panied by the liberation of different gases, was a purely chemical 
process, but it is very doubtful, in the light of our present-day 
knowledge, if this could take place without the intervention of 
bacteria, yeasts, and molds. 
Sugars are among the first substances to be attacked by yeasts 
and molds in their search for food, and, as a rule, they are broken 
up into carbon dioxide and alcohol. This fermentation is perfectly 
familiar to anyone who has ever observed sweet cider changing into 
hard cider, or who has tasted jam or canned fruit which has 
“worked.’' The characteristic flavor in the latter case is due to 
the alcohol, and the frothing in the former is caused by the escap¬ 
ing carbon dioxide. The gas liberated in this way joins the sup¬ 
ply in the air and once more it is ready to be taken up again by 
the leaves of some green plant and made into starch and sugar. 
The alcohol, likewise, passes into the air, under ordinary condi¬ 
tions, and ultimately is oxidized into carbon dioxide and water. 
Some bacteria, also, can accomplish the destruction of sugars. This 
may lead to the production of a number of alcohols, carbon diox¬ 
ide, hydrogen, methane or marsh gas, and several different or¬ 
ganic acids, among which may be mentioned butyric, lactic, acetic, 
