4> Mr. Carlisle's Lecture 
irritable limb sustained a weight one-sixth heavier than the 
dead limb. 
It may be remarked, in confirmation of these experiments, 
that when muscles act more powerfully, or more rapidly, than 
is equal to the strength of the sustaining parts, they do not 
usually rupture their fleshy fibres, but break their tendons, or 
even an intervening bone, as in the instances of ruptured tendo 
Achillis, and fractured patella. Instances have however oc- 
curred, wherein the fleshy bellies of muscles have been 
lacerated by spasmodic actions ; as in tetanus the recti abdo- 
minis have been torn asunder, and the gastrocnemii in cramps ; 
but in those examples it seems that either the antagonists pro- 
duce the effect, or the over-excited parts tear the less excited 
in the same muscle. From whence it may be inferred, that the 
attraction of cohesion in the matter of muscle is considerably 
greater during the act of contracting, than during the passive 
state of tone, or irritable quiescence, a fact which has been 
always assumed by anatomists from the determinate forces 
which muscles exert. 
The muscular parts of different classes of animals vary in 
colour and texture, and not unfrequently those variations occur 
in the same individual. 
The muscles of fishes and vermes are often colourless, 
those of the mammalia and birds being always red : the am- 
phibia, the accipenser, and squalus genera, have frequently 
both red and colourless muscles in the same animal. 
Some birds, as the black game,* have the external pectoral 
muscles of a deep red colour, whilst the internal are pale. 
In texture, the fasciculi vary in thickness, and the reticular 
* Tcirao tetrix. Lin. 
