APPLICATIONS OF MUSCULAR POWER. 453 
many Insects strike the air several hundred times,—and 
those of some of the smaller Insects many thousand times,— 
-in a second of time. 
Applications of Muscular Power :—Bones and Joints. 
595. Muscular contraction performs an important part in 
nearly every one of the functions of which we have already 
treated. Thus the reception of the food, and its propulsion 
along the alimentary canal, forming part of the function of 
im, are accomplished through its means. The Circula- 
tion of the blood, again, depends mainly on the agency of a 
contractile organ, the heart. The Respiration cannot be kept 
up, in the higher animals at least, without the aid of certain 
movements which are accomplished by the muscles. With 
the processes of Nutrition and Secretion it is not so closely 
connected ; but the latter is dependent upon it so far as this, 
that its products are carried out of the body by the aid of 
muscular contraction. And even in Sensation, the peculiar 
endowment of muscular tissue comes into use; by giving to 
the organs of sense those movements which enable them to 
_ take a wider range, and to apply themselves most perfectly to 
_ the objects before them. But we have now to study its appli- 
cations in those general and partial movements of the body, ~ 
on which depend the locomotion (or change of place) of 
_ animals, their attitudes, and a number of other important 
actions, entirely of a mechanical nature. 
596. The organs by which these are effected, may be con- 
veniently divided into the active and passive. The active are 
_ those which have peculiar vital powers within themselves, and 
which exert these in giving motion to other parts. To this 
class, therefore, we refer the Muscles, whose peculiar endow- 
' ments have been just considered. The passive organs, on the 
’ other hand, are those which perform no action of themselves, 
. which have no power but that of yielding a simply mechanical 
support, and which consequently perform no movement but 
_ such as they are made to do by the muscles. Of this kind 
_ are the hard parts which form the skeleton or solid frame- 
_ work of the body, whether this be internal or external. 
597. In the lower tribes of animals, the muscles are all 
_ inserted in the soft and flexible membrane which covers the 
_ body ; and it is by acting upon this, that they can change the 
