20 



Physiology. 



involuntary. The heart muscle fibers are intermediate, 

 being striated, but involuntary in their action. A striated 



muscle fiber may be ij inches 

 long and -^^ of an inch wide, 

 though usually less. The heart 

 muscle fiber is narrower than 

 the striated fiber, and the plain 

 fiber very much smaller than 

 either. (The figures do not 

 attempt to give exact propor- 

 tions.) 



A Muscle Fiber is a Cell. - 



It is easily seen that each plain 

 muscle fiber is a single cell, hav- 

 ing its distinct nucleus. The 



Fig. 15. Muscle Fibers from the Heart, Same is true of the heart milSCle 



^S: d a^]S^ rCrOSSStriae ' ^ers, though they are not so 



The nuclei and cell-junctions are shown simple, being more OF leSS 



only on the right hand side of the 



figure. branched. 



Effect of Cooking Muscle. In well-cooked corned beef 

 the connective tissue is thoroughly softened, and the mus- 

 cle fibers are easily separated. Thorough cooking, espe- 

 cially stewing, will soften the connective tissue, and may 

 make tender meat that, cooked otherwise, would be very 

 tough on account of the large amount of connective tissue. 



Imitation of Structure of Muscle. Take a number of pieces of red 

 cord to represent the muscle fibers. Wrap each in white tissue paper; 

 this represents a single fiber sheath. Lay a number of these side 'by 

 side, and wrap them all in a common sheath. Let the tissue paper pro- 

 ject beyond the ends of the threads, and here compress it into a com- 

 pact cylinder ; this last represents the tendon. 



Connective Tissue the Skeleton of Muscle. If all the 



muscle fibers were removed from a muscle, the sheaths 



