THE ORGANS. 107 



each other, into that intimate correlation that makes them subordi- 

 nate parts of a single organism. 



Through the medium of the circulatory system the exchanges of 

 material essential to the well-being of each organ and of the whole 

 body are made possible, and through the nervous system the activ- 

 ities of the different parts of the body are so regulated that they 

 work in harmony with each other and respond to their collective 

 needs. 



Because of their wide distribution throughout the body, we can 

 hardly study any structures which are not in intimate relations with 

 both vessels and nerves. It will, therefore, be well to consider the 

 structure of the circulatory system before proceeding to a study of 

 other organs. The study of the nervous system must, because of 

 its complexity, be deferred. 



