=Gluten.=--The principal part of the protein in wheat is known as gluten. Gluten as such does not exist in the wheat but is formed when the pulverized wheat, that is, the wheat flour, is mixed with water by the union of two elements in the wheat, namely, gliadin, which is soluble in dilute alcohol and forms nearly half of the whole protein matter of the wheat kernel, and glutenin, a compound insoluble in water, dilute salt solutions, and dilute alcohol and which is quite as abundant as gliadin in the wheat kernel. In fact, the gliadin and the glutenin together make the whole of the protein, except a little over one per cent. There are three other forms of protein, as pointed out by Osborne, in the wheat kernel, making altogether nearly 1¹⁄₂ percent of total protein content. The average quantity of these compounds in the protein of wheat is as follows. Constituents: Globulin, 0.70 percent Albumin, 0.40 „ Proteose, 0.30 „ Gliadin, 4.25 „ Glutenin, 4.35 „ ----- 10.00 =Starch in the Wheat Kernel.=--The most abundant constituent of the wheat kernel is the starch. The appearance of wheat starch is shown in the figure. Wheat starch grains ordinarily show the rings and hilum in a few cases only under the most favorable conditions, though there are sometimes cases where the striations are quite distinct. The granules of starch vary greatly in size, being from 5 to 10 microns in diameter. There are, in fact, two kinds of granules in wheat starch, one having the appearance under the microscope of irregularly rounded particles in sections like a circular disk, and the other of elongated particles with a distinct hilum, as shown in Fig. 32. The appearance of the granules under polarized light is shown in Fig. 33. Wheat starch is not very commonly used for commercial purposes but is highly prized for some things, especially in the sizing of textile fabrics. The germ in wheat is particularly rich in oil and the bran or outside covering in protein. The common idea that the bran is composed mostly of silicious matter is wholly erroneous. On the contrary the bran is a highly nutritious food, and the objection to it for human food is mostly of a mechanical nature. =Adulterations.=--Wheat grains are never adulterated but they may sometimes contain dirt and foreign seeds, due to the growth of some body in connection with the wheat itself. =Standards.=--Wheat, commercially, is sold under three standards, namely, one, two, three. The difference is an arbitrary one and not founded upon any chemical data but wholly upon the physical appearance, degree of moisture, and freedom from extraneous admixtures.