CHAPTER II 



THE GENERAL STRUCTURE OF THE HUMAN 

 BODY 



Definition of Physiology. Although all animals have 

 to procure and digest food, to absorb oxygen and 

 eliminate waste materials, yet the ways in which they 

 accomplish this are so varied as to give rise to many 

 kinds of structure. In accordance with the degree of 

 their complexity, animals may be arranged in a series. 

 At the bottom, we may place the one-celled animal with 

 its simple structure, any part of which is convertible 

 to any use, being interchangeably stomach, lung, foot 

 or excretory organ ; and at the top, man, whose millions, 

 of cells are arranged in groups as organs and tissues,, 

 each group of which is able to do only its own par- 

 ticular work. The study of the structure of animals is- 

 anatomy. The study of the work done by these struc- 

 tures- and the way in which it is done is physiology , 

 That branch of physiology devoted to man is human 

 physiology. 



Man a mammal. Man belongs to the higher class; 

 of animals which have a backbone or vertebral column 

 and which are therefore called vertebrates. Man further 

 belongs to the highest division among vertebrates which 

 suckle their young and because of this are called mam- 

 mals. In structure, man differs from some of the other 

 mammals, especially from the higher apes, only in minor 

 details, He has, for example, shorter arms and a larger 



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