704 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



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cells are arranged in bundles connected by a cement substance ; they do 

 not terminate in tendons, but are arranged in groups, usually in the form 

 of a membrane ; such muscular fibres are found in the walls of the ali- 

 mentary canal, in the walls of the genito-urinary passages, in the bronchi, 

 and in various other localities. 



(a) The Chemical Composition of Muscle. The chemical constit- 

 uents found in muscles differ greatly according as the examination is 

 made on fresh, living tissue, or after rigor mortis has set in. All mus- 

 cles after death lose their irritability, and pass from their flexible, trans- 

 parent condition into a state of rigidity and opacity, which is described 

 under the general term of rigor mortis. Analogy 

 may be traced in this respect between the living 

 and dead muscle and blood. 



Blood in the process of coagulation produces 

 the proteid fibrin ; muscle, in the act of dying, 

 produces the proteid myosin. 



Before taking up the characteristics of these 

 bodies, further comparison of the characteristics 

 of living and dead muscle deserves attention. 



In the first place, in a state of rest, living 

 muscle has an alkaline reaction ; in dead muscle, 

 and in muscle in contraction, the reaction is acid, 

 due to the development of paralactic acid, as well 

 as acid potassium phosphate, and carbonic acid. 



Living muscle is to a certain extent trans- 

 lucent, extensible, and elastic ; dead muscle is 

 opaque, rigid, inextensible, and has lost its elas- 

 ticity. The main difference, however, between 

 living and dead muscle is found in the coagulation 

 of nvyosin in the latter. If a living muscle be 

 freed from blood by repeated washing and injec- 

 tion of saline solution through its blood-vessels, be then frozen, chopped 

 up, and rubbed up in a mortar with four times its weight of powdered 

 ice, containing 1 per cent, of sodium chloride, a mixture is obtained 

 which, below the freezing point, is sufficiently fluid to be filtered. This 

 opalescent filtrate is known as muscle-plasma, and remains fluid only 

 while kept at C. If allowed to be heated above this point it is 

 gradually transformed into a solid jelly, which subsequently separates 

 into a clot and serum. The clot is myosin, and originates in the doubly 

 refractive substance ; the serum contains serum-albumen and various 

 extractives. 



If a muscle which has already passed into the condition of rigor 

 mortis be washed with water so as to remove the albumen and the dif- 



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FIG. 274. PRIMITIVE 

 BUNDLE FROM THE BI- 

 CEPS BRACHII OF THE 

 HORSE. (Tereg.) 



A, intermediary disks : B, cen- 

 tral disks ; C, dark striation ; D, 

 light striatiou. 



