INTRODtJCTORY. 



The animal body is made up of different "organs" having spe- 

 cial functions. These may be either more or less independent an- 

 atomically, or they may be grouped together into systems. The 

 organs of the body and the parts of the systems are composed of 

 different tissues, which in turn consist of cells and special permanent 

 products of the cells — intercellular substance. This analysis may be 

 set forth diagrammatically as follows : 



f ^"-^""^"^ ) ^. (cells 



i systems (of > Tissues. < 



j ' ^ 1 I intercellular substance. 



The fundamental tissues of the body are of four kinds : 



A. Epithelial. Cells only slightly modified structurally and ar- 



ranged in layers or masses; intercellular substance (cell- 

 cement) small in amount and undifiFerentiated. 



B. Connective and Supporting. Cells insignificant in number, 



slightly modified structurally; intercellular substance pre- 

 dominant and variously modified. 



C. Muscular. Cells specialized in structure for the purpose of 



producing movement (i. e., for contracting in one direc- 

 tion). 



D. Nervous. Cells specialized in structure for the purpose of or- 



iginating, transmitting, and transferring "nervous im- 

 pulse. ' ' 



In pursuing the study of Histology the following principles 

 are believed to be the most advantageous: 



I . The study of the different tissues should precede the study 

 of the organs. 



. 2. Every tissue and organ should be studied fresh as far as 

 possible in order to have correct notions of the structural appear- 

 ances unmodified by reagents. 



3. Every tissue and organ should be studied alive as far as 

 possible in order to see the function and thus associate function and 

 structure. 



4. Before the microscopic structure of an organ or part is 

 studied ^h^ gross anatomy should be first thoroughly understood. 



