CHAPTER VII. 



MUSCLES AND PHENOMENA OF CONTRACTION. 



Probably the most striking characteristic of any living 

 body is its ability to move. But this power of motion is by 

 no means a property of all living things. The entire realm 

 of plants, with exceptions of course which need not concern 

 us here, is devoid of the power of actual movement, and 

 there are some animals whose ability to move from place to 

 place is entirely wanting. The movements of our bodies 

 are caused by the contraction of organs familiar to every 

 one as the muscles. There are, however, in the body struc- 

 tures other than the muscles which possess this power to a 

 certain extent. Thus, many of the varieties of white cor- 

 puscles, such as the white blood corpuscles, cartilage cells, 

 connective tissue cells, are able to move from place to 

 place. Such locomotion is described as amoeboid. The 

 power of active movement also occurs in ciliated cells 

 which are found lining the entire respiratory system, with 

 the exception of the pharynx and the internal lung cells, 

 and which occur also in the internal genital ducts. Such 

 cells consist of a main body which shows no power of 

 motion, but is continued at one end into a number of 

 thread-like prolongations, which have the power of moving 

 rapidly backwards and forwards. The expulsion of the 

 phlegm from the respiratory passages up into the mouth is 

 accomplished by such ciliated action. It is interesting to 

 observe that all the cilia of a membrane seem to move in 

 harmony, the movements of the cilia sweeping across the 

 surface like waves of moving grain through a wind-swept 

 wheat field. In the internal genital ducts they serve to 

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