sition, but
differing widely in structural composition. As a class, the proteins
contain about 16 per cent of nitrogen, 52 per cent of carbon, from 6 to
7 per cent of hydrogen, 22 per cent of oxygen, and less than 2 per cent
of sulphur. These elements are combined in a great variety of ways,
forming various groups or radicals. In studying the protein molecule a
large number of derivative products have been observed, as amid
radicals, various hydrocarbons, fatty acids, and carbohydrate-like
bodies.[8] It would appear that in the chemical composition of the
proteins there are all the constituents, or simpler products, of the
non-nitrogenous compounds, and these are in chemical combination with
amid radicals and nitrogen in various forms. The nitrogen of many
proteids appears to be present in more than one form or radical. The
proteids take an important part in life processes. They are found more
extensively in animal than in plant bodies. The protoplasm of both the
plant and animal cell is composed mainly of protein.

Proteids are divided into various subdivisions, as albumins, globulins,
albuminates, proteoses and peptones, and insoluble proteids. In plant
and animal foods a large amount of the protein is present as insoluble
proteids; that is, they are not dissolved by solvents, as water and
dilute salt solution. The albumins are soluble in water and coagulated
by heat at a temperature of 157 deg. to 161 deg. F. Whenever a food material is
soaked in water, the albumin is removed and can then be coagulated by
the action of heat, or of chemicals, as tannic acid, lead acetate, and
salts of mercury. The globulins are proteids extracted from food
materials by dilute salt solution after the removal of the albumins.
Globulins also are coagulated by heat and precipitated by chemicals. The
amount of globulins in vegetable foods is small. In animal foods myosin
in meat and vitellin, found in the yolk of the egg, and some of the
proteids of the blood, are examples of globulins. Albuminates are
casein-like proteids found in both animal and vegetable foods. They are
supposed to be proteins that are in feeble chemical combination with
acid and alkaline compounds, and they are sometimes called acid and
alkali proteids. Some are precipitated from their solutions by acids and
others by alkalies. Peas and beans contain quite large amounts of a
casein-like proteid called legumin. Proteoses and peptones are proteins
soluble in water, but n