CHAPTER IV 

 CONTRACTILE TISSUES 



It is a peculiar fact about physiology that very diflensnt 

 orders of presentation have commended themselves to 

 different writers and have been used with success. 

 Whatever one chooses to place first, one is likely soon to 

 wish that the student were in possession of some other 

 part of the subject to serve him as a background* But 

 there is much to be said in favor of the introduction 

 early in a book of the physiology of movement. We 

 have to reckon with it in all the remaining sections of our 

 survey. So in the present instance we shall take up the 

 question of motion at this time. 



It has been said previously that most of the 

 executed by Animal cells are the expression of < 

 as that term is understood by the biologist. Such move- 

 ments may be carried out by single cefls or by tissues 

 composed of cefls whose action is concerted. We could 

 know nothing about the behavior of single cefls if we 

 had not the ^nninLmny of th** microscope. Thanks to 

 that instrument we have found out that the two ex- 

 hibitions of contractility which are most common 

 among one-celled animal forms are to be seen also in the 

 higher organisms. These are, respectively, 

 ciliary movement. 



Ameboid Movement. This manffffliion of the 

 tractile property takes its name from a 

 aquatic amimailj the ^mribjt. It is one of 

 types conceivable, a minute mass of jeDy-tike 

 with a nucleus which confirms its light to rank as a 

 It is usually colorless and transparent *"*M"pi for 

 oos granules within. Its movement 



53 



