THE MICROSCOPE. 241 
alcohol, coagulates the proteids of the muscles, but. it also swells up 
the connective tissue), 33 per cent. alcohol .* 
With insects, e. g., cockroach and dytiscus, the reagent may be 
injected into the body cavity, or the insect, e. g., a caterpiller, may 
be placed whole into the reagent. In both of these cases, some 
fibers may be usually found with fixed local contraction waves. A 
convenient way of obtaining fixed contraction waves is in many cases 
by tearing out a leg and placing the protruding fibers into osmic 
acid ().5 per cent., or into absolute alcohol. Good specimens may be 
thus obtained from the crawfish. In such specimens, note carefully 
the appearances of the bands as the microscope is gradually lowered 
from the highest to the lowest point at which the bands are visible. 
Hardened fibers may be stained in hematoxylin or eosin, 
MUSCLE FIBERS IN POLARIZED LIGHT. 
To observe the singly and doubly refracting parts of muscle 
fibers, take an animal, such as hydrophilus, in which the bands are 
broad, stretch out one of its muscles and place it in 50 per cent. 
alcohol for a day, then gradually increase the strength of the 
alcohol until it is absolute. Tease out a few fibers on a slide, clear 
with clove oil, and mount in C. balsam. Only those fibers in which 
the planes of the discs are at right angles to the plane of the glass 
should be observed. — 
If fresh fibers are treated with dilute acids, alkalis or ammo- 
nium chloride (as above), and then hardened, the doubly refracting 
substance will be found to have largely disappeared. The fibers do 
not lose their doubly refracting power on boiling, provided they are 
kept extended. (Nasse.) 
VARIETIES IN THE FORM OF MUSCULAR FIBERS. 
Take the heart of a sheep, as fresh as possible, and carefully 
examine the endocardium of the ventricle, certain transparent, jelly- 
like lines and spaces, and carefully remove the isolated piece of 
endocardium, removing as far as possible the subjacent cardiac 
muscle fibers. Purkinjes’ cells will be found in the connective tissue 
of the endocardium. The cells may be isolated by 33 per cent. 
alcohol, and stained with picro-carmine. 
Branched striated muscle fibers may be seen in the tongue of 
the frog. 
Fresh muscle fibers, when warmed with dilute acids or dilute 
alkalis, are partially dissolved, the dim band being chiefly affected. 
The solution of the substances of the dim band is still more marked 
* When a muscle cannot conveniently be extended, a concentrated aqueous solution 
of boracic acid may be used. This does not coagulate the proteids of muscle, and causes 
little or no shrinking. (Wasse.) 
