=Active Principles Contained in Meat Extract.=--Attention has already been called to some of the more important active principles, namely, meat bases which form a valuable portion of meat extract. There are various forms of nitrogenous bodies, however, besides meat bases, which become soluble naturally in meat or by the treatment of meat with digestive ferments. Lean meat, as is well known, consists almost exclusively of protein matter and water. This protein matter is principally insoluble. Under the action of digestive ferments the protein of meat becomes broken up into more soluble bodies, known as albumoses, proteoses and peptones,--the latter being the final product of solution. These bodies are still true protein bodies containing the elements of sulfur as one of their essential constituents. The meat bases, on the contrary, contain the other elements that are in protein but do not have the sulfur element. They belong to that class of bodies which is known as simple amido compounds. All of these bodies are mixed together in meat juice or beef extract, and it is an important task of the chemist to separate them, both from an analytical point of view and the determination of their relative abundance. There is also another soluble or semisoluble protein substance in these extracts derived from the tendinous tissues and bones, namely, the gelatine or glue. This is quite a common product, being the soluble protein procured by the digestion of the tendons and bones. It is important, therefore, that the chemist should distinguish between the gelatine and the amido bodies. There is also a true and a false protein form of these soluble bodies, the true one being formed by natural proteolytic ferments and the false one being formed by heat or digestion under pressure of steam. The chemist should also be able to distinguish between the true extract formed directly from the meat and the yeast extract used as an adulteration. It is not the purpose of this manual to enter into the details of how these different bodies may be distinguished from one another, as that is purely a chemical study. It is due, however, to the general reader that some explanation be given of the different classes of bodies which are contained in these extracts.