194 NATURAL THEOLOGY. 



familiar as this action is, and simple as it seems 

 to be, how many things are requisite for the per- 

 forming of it ; how many things which we under- 

 stand, to say nothing of many more, probably, 

 which we do not : viz., first, a long, hard, strong 

 cylinder, in order to give to the arm its firmness 

 and tension ; but which, being rigid, and, in its 

 substance, inflexible, can only turn upon joints ; 

 secondly, therefore, joints for this purpose ; one 

 at the shoulder to raise the arm, another at the 

 elbow to bend it ; these joints continually fed 

 with a soft mucilage to make the parts slip easily 

 upon one another, and holden together by strong 

 braces, to keep them in their position : then, 

 thirdly, strings and wires — i. e., muscles and ten- 

 dons — artificially inserted, for the purpose of 

 drawing the bones in the directions in which the 

 joints allow them to move. Hitherto we seem to 

 understand the mechanism pretty well ; and, un- 

 derstanding this, we possess enough for our con- 

 clusion : Nevertheless, we have hitherto only a 

 machine standing still — a dead organization — an 

 apparatus. To put the system in a state of ac- 

 tivity, to set it at work, a further provision is 

 necessary — viz., a communication with the brain 

 by means of nerves. We know the existence of 

 this communication, because we can see the com- 

 municating threads, and can trace them to the 

 brain : its necessity we also know, because if the 

 thread be cut, if the communication be intercept- 

 ed, the muscle becomes paralj^ic ; but beyond 



