A TEXT-BOOK 



OF 



PHYSIOLOGY 



SECTION I. 

 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



CHAPTER I. 

 THE PHENOMENON OF CONTRACTION. 



The tissues in the mammalian body in which the property of 

 contractility has been developed to a notable extent are the mus- 

 cular and the ciliated epithelial cells. The functional value of the 

 muscles and the cilia to the body as an organism depends, in fact, 

 upon the special development of this property. The muscular 

 tissues of the body fall into three large groups, considered from 

 either a histologicalor a functional standpoint, namely, the striated 

 skeletal muscle, the striated cardiac muscle, and the plain muscle. 

 These tissues exhibit certain marked differences in properties which 

 are described farther on. In each group, moreover, there are 

 certain minor differences in structure which are associated with 

 differences in properties; thus, skeletal muscle from different re- 

 gions of the same animal may show variations in rapidity of 

 contraction, and this variation goes hand in hand with an obvious 

 difference in histological structure. Similar, perhaps more 

 marked, differences are observed in the plain muscular tissue of 

 various organs. The muscular tissues from animals belonging to 

 different classes exhibit naturally even wider variations in proper- 

 ties, and these differences in some cases are not associated with 

 visible variations in structure. 



The Structure of Skeletal Muscle. This tissue makes up the 

 essential part of the skeletal muscles by means of which our 

 2 17 



