Each fiber is enclosed in the sarcolemma, a thin, elastic membrane. A
thin, delicate band occurring regularly along the length of the fiber divides
the fiber into its structural units, the sarcomeres, a fiber being composed
of a succession of sarcomeres. A dark band shows in the middle of each
sarcomere, a lighter band on either side. The material between the fibrils is
known as the sarcoplasm and the relative amount of sarcoplasm varies in
muscles of different animals.
The contracting tissue, the fibrils, run the length of the fiber. The fibrils
consist of alternating light and dark segments which form the cross
striations of the fibers. See Figs. 21 and 22. The cross bands are supposed
to be of denser structure than the material between these bands. Fig. 22
shows the immense number of these cross striations. The cross striations
also show plainly in the fibers of Fig. 21.
All the material within the sarcolemma is known as the muscle plasma
and in the living muscle is in a semi-liquid state.
Effect of exercise and maturity upon fibers. Beard in his study of ''Tough
and Tender Meat" states that ''muscle fibers attain their maturity by use
and age. Development implies increase in size rather than maturity." Beard
made a microscopic study of different muscles of five different animals. The
animals selected for study were a heifer, a short-fed steer, a prime steer, an
-old cow, and a veal calf. Some of his observations and conclusions are as
follows :
"Connective tissue seems more apparent in thinner fleshed beef.
"There was intracellular fat (fatty degeneration) in the fat steer.
THE MUSCLE FIBERS
207
"The fat steer had more intrafascicular, intercellular fat than any
animals studied.
"The inherent properties of the endomysium contribute to the toughness
of meat more than does the size of the fiber.
"The muscle fibers from the region of the toughest meat contain the
densest sarcoplasm, while fibers from the tenderest muscles contain the
lightest sarcoplasm.
"Intramuscular and particularly intrafascicular fat lessens the toughness
of meat.
Courtesy of Fred J. Beard, lozva State College
Fig. 22. — Longitudinal section of muscle fibers of beef, showing cross striations.
Magnification approximately x 1400.
"Where only a small amount of intramuscular fat is found it is almost
always interfascicular. As the interfascicular fat increases in amount
intrafascicular fat appears which is first intercellular and in case of exces-
sive adiposity intracellular also."
Beard states that "while those muscles which are brought most into
activity and those performing the greatest amount of work may not possess
a larger fiber than those muscles which are less active, the more active
muscles do have a thicker perimysium and apparently more substance in
the fiber, as manifested in the staining characters of the sections."
Toughness of meat. Since meat is composed of muscle fibers and con-
nective tissue, toughness of meat must be due to either of these, or to both.
Toughness of connective tissue depends upon the proportion of elastin
and collagen; upon the thickness or density of the tissue, which is brought
208
MEAT
Page 165
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Each fiber is enclosed in the sarcolemma, a thin, elastic membrane. A
thin, delicate band occurring regularly along the length of the fiber divides
the fiber into its structural units, the sarcomeres, a fiber being composed
of a succession of sarcomeres. A dark band shows in the middle of each
sarcomere, a lighter band on either side. The material between the fibrils is
known as the sarcoplasm and the relative amount of sarcoplasm varies in
muscles of different animals.
The contracting tissue, the fibrils, run the length of the fiber. The fibrils
consist of alternating light and dark segments which form the cross
striations of the fibers. See Figs. 21 and 22. The cross bands are supposed
to be of denser structure than the material between these bands. Fig. 22
shows the immense number of these cross striations. The cross striations
also show plainly in the fibers of Fig. 21.
All the material within the sarcolemma is known as the muscle plasma
and in the living muscle is in a semi-liquid state.
Effect of exercise and maturity upon fibers. Beard in his study of ''Tough
and Tender Meat" states that ''muscle fibers attain their maturity by use
and age. Development implies increase in size rather than maturity." Beard
made a microscopic study of different muscles of five different animals. The
animals selected for study were a heifer, a short-fed steer, a prime steer, an
-old cow, and a veal calf. Some of his observations and conclusions are as
follows :
"Connective tissue seems more apparent in thinner fleshed beef.
"There was intracellular fat (fatty degeneration) in the fat steer.
THE MUSCLE FIBERS
207
"The fat steer had more intrafascicular, intercellular fat than any
animals studied.
"The inherent properties of the endomysium contribute to the toughness
of meat more than does the size of the fiber.
"The muscle fibers from the region of the toughest meat contain the
densest sarcoplasm, while fibers from the tenderest muscles contain the
lightest sarcoplasm.
"Intramuscular and particularly intrafascicular fat lessens the toughness
of meat.
Courtesy of Fred J. Beard, lozva State College
Fig. 22. — Longitudinal section of muscle fibers of beef, showing cross striations.
Magnification approximately x 1400.
"Where only a small amount of intramuscular fat is found it is almost
always interfascicular. As the interfascicular fat increases in amount
intrafascicular fat appears which is first intercellular and in case of exces-
sive adiposity intracellular also."
Beard states that "while those muscles which are brought most into
activity and those performing the greatest amount of work may not possess
a larger fiber than those muscles which are less active, the more active
muscles do have a thicker perimysium and apparently more substance in
the fiber, as manifested in the staining characters of the sections."
Toughness of meat. Since meat is composed of muscle fibers and con-
nective tissue, toughness of meat must be due to either of these, or to both.
Toughness of connective tissue depends upon the proportion of elastin
and collagen; upon the thickness or density of the tissue, which is brought
208
MEAT