THe MICROSCOPE. 81 
PIPE MWe NAR Y. “DE PARTMENT 
A COURSE IN ANIMAL HISTOLOGY. 
NINTH PAPER. 
FRANK W. BROWN, M. D. 
USCLE.—There are three forms of muscle: (1) Striated, or 
voluntary, (2) Non-striated, or involuntary, and (8) Cardiac, 
muscle. 
Srriatep Muscie.—Take a shred of muscle from the leg of a 
frog or other animal, tease out thoroughly in the salt solution, and 
examine with alow power. The fibers, having a diameter of about 
=4, of an inch, are easily made out. Careful search will show parts 
of these fibers transversely marked or striated. These striations are 
very characteristic and should be studied. Examining at different 
foci, it will be seen that the striz run clear through the fiber. Once 
recognized, they ought never to be mistaken for anything else. Less 
marked and less numerous are the longitudinal striations, generally 
found where the cross striations are not visible. Certain fibers may 
show no cross striations, but may appear like bundles of fibrous tis- 
sue, owing to the existence of numerous longitudinal markings. 
These longitudinal markings show the divisions of the fiber into 
primitive fibrils. With a somewhat higher power study the ends of 
the fibers or parts in its course where the muscle substance has been 
injured. A homogeneous membrane may be found. This mem- 
brane—the sarcolemma, invests each muscle fiber. It is apparently 
structureless and highly elastic. Irrigate the specimen with dilute 
acetic acid. The striations become more prominent and numbers of 
spindle-shaped nuclei appear. These nuclei are situated just under 
the sarcolemma and are attached to it. Whether they are small, 
connective-tissue corpuscles belonging to the sarcolemma, or whether 
they are muscle nuclei is a question. Probably they are muscle 
nuclei, for in certain muscle (the red muscle of many animals) they 
are embedded in the muscular substance and are detached from the 
sarcolemma. 
Place a portion of muscle in a solution of chromic acid (51, 
where it should be left to harden. When teased out in the salt solu- 
tion it will be seen that the fibers have become split up into primi- 
tive fibrils. The cross markings are still visible on the fibrils. 
Put another portion into an aqueous solution of HCl (;4,). 
The fibers will be divided along the line of the cross striations, form- 
ing little plates or dises—Bowman’s discs. 
