186 ANIMAL PHYSIOLOGY. 
THE CHANGES IN A MUSCLE DURING CONTRACTION, 
Though the change in form is very great during the con- 
traction of a muscle, the change in bulk is almost inappreci- 
able, amounting to a diminution of not more than about a4 
of the volume. In fact, according to the latest investigator, 
there is no diminution whatever. A series of levers may be 
laid on a muscle or the columns of air in a series of Marey’s 
tambours may be influenced by the contracting muscle, and 
from some such apparatus a graphic record like that seen in 
Fig. 183 may be obtained. 
It is to be observed that the contraction passes along the 
muscle in the form of a wave, the size and speed of which are 
Qo 
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ALLE LIL POLIS FT 
Fia. 183.—Tracing of the propagation of the muscular wave. Chronographic tracing, one 
hundred vibrations per second underneath (Marey). 
susceptible of measurement. For the frog the wave-length is 
estimated at from 200 to 400 mm., and the velocity at about 3 
to 4 metres per second. 
It is probably rather greater in the muscles of mammals 
and greater under the more natural conditions of the muscle in 
the intact living body. 
But since the fibers of striped muscle are of very limited 
length (30 to 40 mm.), it would seem that a contraction origi- 
nating in one fiber must be capable of initiating a similar 
action in its neighbor; and, as the ends of the fibers lie in con- 
tact, it is easy to understand how the wave of contraction 
spreads. Normally, the contraction must pass from about the 
center of the muscle-cell where the nerve terminates in the 
end-plate. 
The microscopic changes occurring in contracting muscle 
are not well understood. The living muscle of a beetle’s thigh 
when placed under a microscope may be seen in contraction—a 
sight of the most striking nature, reminding one of a billowy, 
tempestuous sea, and by the use of reagents the waves of con- 
traction may be fixed. 
It may be stated that the parts distinat before remain so 
