43. Ultimate Composition Of Proteins

The ultimate composition of the proteins, that is, the proportions of the elements which they contain, has been carefully studied, and while there are material differences among them in this respect, the limits of variation are not especially wide, as can be seen from the following figures taken from Neumeister: -

Table XIII. Elementary Composition Of The Proteins

We see that the number of elements ordinarily found in the proteins is five, nitrogen and sulfur being those that chiefly distinguish these bodies from all others which make up the mass of combustible matter. Two other elements are found in certain of these bodies, as, for instance, phosphorus in casein and iron in a constituent of blood.

44. . Familiar Examples Of Proteins

Proteins are familiar objects in the home, and their properties are matters of common observation. When the farmer's boy secures the tenacious cud of gum from the fresh wheat gluten, or when the housewife watches the strings of coagulated albumin separate from the cold water extract of fresh lean beef that is brought to the boiling point, or observes the white of an egg harden into a tough, white mass as it is dropped into boiling water; when we note the stiffening of the muscular tissue of the slaughtered animal or the rapid formation of strings of fibrin in the cooling blood, - in all these instances there are manifested certain chemical or physical properties which pertain to these most important and useful compounds.