eed from its oxygen
it takes a purple hue; hence the widely different appearance of arterial
and venous blood, which so puzzled the early physiologists.

This proof of the vitally important role played by the red-blood
corpuscles led, naturally, to renewed studies of these infinitesimal
bodies. It was found that they may vary greatly in number at different
periods in the life of the same individual, proving that they may be
both developed and destroyed in the adult organism. Indeed, extended
observations left no reason to doubt that the process of corpuscle
formation and destruction may be a perfectly normal one--that, in
short, every red-blood corpuscle runs its course and dies like any more
elaborate organism. They are formed constantly in the red marrow of
bones, and are destroyed in the liver, where they contribute to the
formation of the coloring matter of the bile. Whether there are other
seats of such manufacture and destruction of the corpuscles is not
yet fully determined. Nor are histologists agreed as to whether the
red-blood corpuscles themselves are to be regarded as true cells, or
merely as fragments of cells budded out from a true cell for a special
purpose; but in either case there is not the slightest doubt that the
chief function of the red corpuscle is to carry oxygen.

If the oxygen is taken to the ultimate cells before combining with
the combustibles it is to consume, it goes without saying that these
combustibles themselves must be carried there also. Nor could it be in
doubt that the chiefest of these ultimate tissues, as regards, quantity
of fuel required, are the muscles. A general and comprehensive view
of the organism includes, then, digestive apparatus and lungs as the
channels of fuel-supply; blood and lymph channels as the transportation
system; and muscle cells, united into muscle fibres, as the consumption
furnaces, where fuel is burned and energy transformed and rendered
available for the purposes of the organism, supplemented by a set of
excretory organs, through which the waste products--the ashes--are
eliminated from the system.

But there remain, broadly speaking, two other sets of organs whose size
demonstrates their importance in the economy of the organism, yet
whose functions are not accounted for in this synopsis. These are those
glandlike organs, such as the spleen, which have no ducts and produce no
visible secretions, and the nervous mechanism, whose central organs are
the