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590 MUSCLES.
diminishes, water is given off, and a re-imbibition takes place and the
so-called " solution of the rigor " appears (v. Furth and Lenk).
The ordinary rigor is an acid rigor and the same applies, according
to Meigs,1
to the water rigor as a shortening of the muscles takes place
when placed in distilled water, by a formation of lactic acid, and because
when such a muscle is placed in Ringer’s solution the acid is removed
and the muscle again expands.
The views are rather contradictory in regard to the production of heat
rigor. According to v. Furth this rigor depends upon the coagulation
of certain proteins, and its occurrence at lower temperatures in cold-
blooded as compared with warm-blooded animals is due, according to
v. Furth, to the fact that in the first a soluble myogen fibrin occurs
preformed in the muscle which coagulates at 30-40° C, while in the
warm-blooded animals the coagulating substance is musculin (myosin
of v. Furth) which coagulates at a higher temperature. According
to Inagaki 2 the various stages in contractions occurring on heating a
muscle (frog) do not correspond to those of the coagulation of the pro-
tein which would occur on heating the muscle plasma, and Meigs has
arrived at a similar view. It must be remarked that also a lactic acid
formation takes place on heating a muscle, and this prevents an exact
comparison of the coagulation of the proteins within and outside
of the muscle. The observations of Vernon that the striated and
the smooth muscles on heating to between 40 and 50° behave differently,
in that the striated become shorter and the smooth become longer,
while both kinds become shorter at higher temperatures, indicates against
a coagulation at these low temperatures. According to Meigs 3
we must
here also admit of an imbibition rigor, due to the formation of lactic acid,
and the different behavior of the two kinds of muscle depends upon a
different arrangement of their anatomical elements.
The chemical rigor produced by different chemically active substances
is also produced, according to Meigs as well as to v. Furth and Lenk,
upon a formation of acid, causing a chemical damage of the muscles, and
is to be considered as an iml ibition rigor.
As it is now generally admitted that the formation of lactic acid dur-
ing the death of the muscle is the cause of the muscle rigor, the question
arises, from what constituents of the muscle is this acid derived? The
most probable explanation is that the lactic acid is produced from the
glycogen, as certain investigators, such as Nasse and Werther, have
observed a decrease in the quantity of glycogen in rigor of the muscle.
1
Journ. of Physiol., 39.
2
Inagaki, Zeitschr. f. Biol., 48; Meigs, Journ. of Physiol., 24.
3
Vernon, Journ. of Physiol., 24; Meigs, Amer. Journ. of Physiol., 24.
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