CHAPTER IX 

 HUMAN TISSUES 



Bone cells build skeletons. Skeletons of fish and frog. 



How can the minute structure of the body he investigated f How is 

 division of labor performed by the human body? What are bone and 

 cartilage f How are the cells in a multicellular organism held together f 



If a thin slice of any portion of the human body is examined 

 microscopically, it will be found to consist of a mosaic of minute 

 units called cells. It will be further found that no cell conforms to 

 the diagram of the typical cell. There are masses of similar cells 

 that build tissues, and these tissues build more complex structures 

 called organs. Each organ has a special duty or function. In 

 the human body there is greater specialization than in the higher 

 plant. Each tissue or group of cells is adapted to perform a par- 

 ticular physiological function. At the same time, all the functions 

 necessary for life are carried on within each cell. 



The cell the unit of structure. Any function of an organism 

 must be considered in relation to the function of tissues or of cells, 

 because it is the individual cell that does the work. Fundamen- 

 tally, each cell possesses the complete apparatus for life. Tissues 

 can be compared to collections of single-celled organisms in that 

 they perform most of the functions that the one-celled animals 

 carry on ; but each group of tissue cells is fitted by shape, structure, 

 location, or chemical powers to perform special functions necessary 

 to the life of the complete organism of which it is a part. There- 



WH. FITZ. AD. BIO. — 6 73 



