I.--The Chemistry of Blood-Making_

Physiologists conceive that the various organs in the body have
originally been formed from blood. If this be admitted, it is obvious
that those substances alone can be considered nutritious that are
capable of being transformed into blood.

When blood is allowed to stand, it coagulates and separates into a
watery fluid called serum, and into the clot, which consists principally
of fibrine. These two bodies contain, in all, seven elements, among
which sulphur, phosphorus, and nitrogen are found; they contain also the
earth of bones. The serum holds in solution common salt and other salts
of potash and soda, of which the acids are carbonic, phosphoric, and
sulphuric acids. Serum, when heated, coagulates into a white mass called
albumen. This substance, along with the fibrine and a red colouring
matter in which iron is a constituent, constitute the globules of blood.

Analysis has shown that fibrine and albumen are perfectly identical in
chemical composition. They may be mutually converted into each other. In
the process of nutrition both may be converted into muscular fibre, and
muscular fibre is capable of being reconverted into blood.

All parts of the animal body which form parts of organs contain
nitrogen. The principal ingredients of blood contain 17 per cent. of
nitrogen, and there is no part of an active organ that contains less
than 17 per cent. of this element.

The nutritive process is simplest in the case of the carnivora, for
their nutriment is chemically identical in composition with their own
tissues. The digestive apparatus of graminivorous animals is less
simple, and their food contains very little nitrogen. From what
constituents of vegetables is their blood produced?

Chemical researches have shown that all such parts of vegetables as can
afford nutriment to animals contain certain constituents which are rich
in nitrogen; and experience proves that animals require for their
nutrition less of these parts of plants in proportion as they abound in
the nitrogenised constituents. These important products are specially
abundant in the seeds of the different kinds of grain, and of peas,
beans, and lentils. They exist, however, in all plants, without
exception, and in every part of plants in larger or smaller quantity.
The nitrogenised compounds of vegetables are called vegetable fibrine,
vegetable albumen, and vegetable casein. All other nitrogenised
compounds occurrin