134 NATURE AND LIFE. 
constant burning—they are every instant receiving oxygen, 
which brings about alterations of various kinds in the depth 
of their substance. In a word, every organ breathes at all 
its points at once, and breathes in its special way. Certain 
physiologists of the present day are wrong in localizing the 
phenomena of breathing in the capillary vessels. They are 
merely the channels of transfer for oxygen, which, by exos- 
mosis, penetrates their thin walls, and then effects, by di- 
rect contact with the smallest particles of the organized 
mass, the chemical action which keeps up the fire of life. 
It is easy to prove this by placing any tissue, lately de- 
tached from the body, in an oxygenated medium. We re- 
mark in this case an escape of carbonic acid, together with 
a development of heat, and this possibility of breathing 
outside the system proves clearly that such act can be ac- 
curately compared, as Lavoisier thought, to the combustion 
of any substance. The only difference is with regard to in- 
tensity. While a candle ora bit of wood burns rapidly, 
with a flame, the combustible materials of organic pulp 
unite with oxygen in a more slow and ‘quiet manner, less 
violently and manifestly. 
The blood, which flows and reflows incessantly in the 
most slender vessels of our bedies, and charges itself full 
with oxygen every time the chest heaves, is composed of 
very various substances. It contains mineral salts, such 
as chlorures, sulphates, phosphates of potassium, soda, 
lime, magnesia, coloring-matters, fatty particles, neutral 
substances of the nature of starch, and nitrogenized prod- 
ucts, such as albumen and fibrin. The salts undergo slight 
changes in the torrent of circulation; they are eliminated 
by the chief emunctories. The neutral matters of the na- 
ture of starch are converted into glycogene and fat. The 
fatty particles undergo in the blood only such oxidizations 
as produce certain derivatives of the same order. And, 
last, the nitrogenized products are made over into fibrin, 
