CHEMISTRY OF MUSCLE. 445 



of the fibre, or with the other short nuclei seen in such numbers 

 between the fibres, which indicate the position of the capillary 

 vessels. 



It is stated that each striated muscle fibre has a nerve fibre 

 passing directly into it, but the exact details of the mode of union 

 in mammalia are not yet satisfactorily made out. 



PROPERTIES OF MUSCLE IN THE PASSIVE STATE. 



Consistence. The contractile substance of muscle is so soft as 

 to deserve rather the name fluid than solid ; it will not drop as a 

 liquid, but its separated parts will flow together again like a half- 

 melted jelly. In this respect it resembles the protoplasm of ele- 

 mentary organisms, the buds from which are so soft that they can 

 unite around foreign bodies, and yet have sufficient consistence 

 to distinguish them from fluid. 



Chemical Composition. The chemical composition of the con- 

 tractile substance of muscle in the living state is not accurately 

 known. The death of the tissue is accompanied by certain 

 changes of a chemical nature which give rise to a kind of coagu- 

 lation, resulting in the formation of two substances, viz., muscle 

 serum and muscle clot or myosin. This coagulation can be post- 

 poned almost indefinitely in the contractile substance of the 

 muscle of cold-blooded animals, by keeping the muscle after its 

 removal at about 5 C. In this way, a pale yellow, opalescent, 

 alkaline juice may be pressed out of the muscle and separated on 

 a cold filter. This substance turns to a jelly at freezing point, 

 and on being allowed to come to the ordinary temperature of the 

 room it passes through the stages of coagulation seen in the 

 contractile substance of dead muscle, and gives the same fluid 

 serum and clot of myosin. Since a frog's muscle can be frozen 

 and thawed without the tissue being killed, it is supposed that, 

 the thick juice is really the contractile substance, and it has been 

 called muscle plasma. 



The coagulation of muscle plasma reminds us in many ways of 

 the clotting of the blood plasma, but the muscle clot, or myosin, 

 which is gelatinous and not in threads like fibrin, is a globulin, 

 and is soluble in ten per cent, solution of salt. It is readily 



