insoluble
proteids. The larger portion of the protein of meats and cereals is in
insoluble forms. The meat juices, which contain the soluble portion of
the proteins, constitute less than 5 percent of the nitrogenous
compounds. Meats contain less amid substances than plants, in which the
amids are produced from ammonium compounds and are supposed to be
intermediate products in the formation of proteids, while in the animal
body they are derived from the proteids supplied in the food and, it is
generally believed, cannot form proteids. Albuminoids make up the
connective tissue, hair, and skin, and are more abundant in animal than
in plant tissue. One of the chief albuminoids is gelatine. Both plant
and animal foods undergo bacterial changes resulting in the production
of alkaloidal bodies known as ptomaines, of which there are a large
number. These are poisonous and are what cause putrid and stale meat to
be unwholesome. The protein in meat differs little in general
composition from that of vegetable origin; differences in structure and
cleavage products between the two are, however, noticeable.

[Illustration: FIG. 26.--MEAT AND EXTRACTIVE SUBSTANCES.]

While meats from different kinds of animals have somewhat the same
general composition, they differ in physical properties, and also in the
nature of the various nutrients. For example, pork contains less protein
than beef, but the protein of pork is materially different from that of
beef, as a larger portion is in the form of soluble proteids, while in
beef more is present in an insoluble form. Not only are differences in
the percentage of individual proteins noticeable, but there are equally
as great differences in the fats. As for example: some of the meats have
a larger proportion of the fat as stearin than do others. Hence meats
differ in texture and taste more than in nutritive value, due to the
variations in the percentage of the different proteins, fats, and
extractive material, rather than to differences in the total amounts of
these compounds. The taste and flavor of meat is to a large extent
influenced by the amount of extractive material.

While the nutrients of meats are divided into classes, as proteins and
fats, there are a large number of separate compounds which make up each
of the individual classes, and there are also small amounts of
compounds which are not included in these groups.

[Illustration: FIG. 27.--STANDARD CUTS OF BEEF.

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