THE TISSUES 4I 



7. The Colour of Muscle varies considerably, some muscles 

 being very pale, almost white in colour e.g. the breast muscles 

 of the fowl; others again being distinctly red, even after all the 

 blood has been removed. This red colour is, in some cases, due 

 to the presence of the pigment of blood, hcemoglobin, but in 

 certain muscles it is due to a peculiar set of pigments, 

 Myohsematins, giving different reactions from the blood 

 pigment. 



3. Physical Characters of Muscle 



1. Muscle is translucent during life, but, as death stiffening 

 sets in, it becomes more opaque. 



2. Muscle is markedly extensile and elastic. A small force 

 is sufficient to change its shape, but when the distorting force 

 is removed it returns completely to its original shape, provided 

 always that the distortion has not overstepped the limits 

 of elasticity. 



When a distorting force is suddenly applied to muscle e.g. if 

 a weight is suddenly attached the distortion takes place at 

 first rapidly, and then more slowly, till the full effect is pro- 

 duced. If now the distorting force is removed the elasticity 

 of the muscle brings it back to its original form, at first rapidly, 

 and then more slowly. {Practical Physiology.} 



The advantages of these properties of muscle are, that every 

 muscle in almost all positions of the parts of the body is 

 stretched between its point of origin and insertion. When it 

 contracts it can therefore act at once to brins about the 

 desired movement, and no time is lost in preliminary tightening. 

 Again, the force of contraction, acting through such an elastic 

 medium, causes the movement to take place more smoothly, and 

 without jerks. Experimentally, too, it has been ascertained 

 that a force acting through such an elastic medium produces 

 more work than when it acts through a rigid medium. 



The extensibility of muscle is of value in allowing a group 

 of muscles to act without being strongly opposed by their 

 antagonistic group. For instance, suppose the extensor muscles 

 of the arm were not readily extensile, when the flexors acted, a 

 large amount of their energy would have to be employed 

 in elongating the extensors. Similarly the elasticity of the 



