The principal proteids of animal origin have their corresponding proteids
in the vegetable kingdom. Some kinds, whether of animal or vegetable
origin, are more easily digested than others. They have the same
physiological value from whichever kingdom they are derived.
The Osseids comprise ossein, gelatin, cartilage, &c., from bone, skin,
and connective issue. They approach the proteids in composition, but
unlike them they cannot form flesh or fulfil the same purpose in
nutrition. Some food chemists wish to call the osseids, albuminoids; what
were formerly termed albuminoids to be always spoken of as proteids only.
Jellies are of little use as food; not only is this because of the low
nutritive value of gelatin, but also on account of the small quantity
which is mixed with a large proportion of water.
The Vegetable Kingdom is the prime source of all organic food; water,
and to a slight extent salts, form the only food that animals can derive
directly from the inorganic kingdom. When man consumes animal food--a
sheep for example--he is only consuming a portion of the food which that
sheep obtained from grass, clover, turnips, &c. All the proteids of the
flesh once existed as proteids in the vegetables; some in exactly the same
chemical form.
Flesh contains no starch or sugar, but a small quantity of glycogen. The
fat in an animal is derived from the carbohydrates, the fats and the
proteids of the vegetables consumed. The soil that produced the herbage,
grain and roots consumed by cattle, in most cases could have produced food
capable of direct utilisation by man. By passing the product of the soil
through animals there is an enormous economic loss, as the greater part of
that food is dissipated in maintaining the life and growth; little remains
as flesh when the animal is delivered into the hands of the butcher. Some
imagine that flesh food is more easily converted into flesh and blood in
our bodies and is consequently more valuable than similar constituents in
vegetables, but such is not the case. Fat, whether from flesh or from
vegetables is digested in the same manner. The proteids of flesh, like
those of vegetables, are converted into peptone by the digestive
juices--taking the form of a perfectly diffusible liquid--otherwise they
could not be absorbed and utilised by the body. Thus the products of
digestion of both animal and vegetable proteids and fats are the same.
