CHAPTER I 

 THE ELEMENTARY TISSUES 



A brief introduction to the histology, or cellular architecture, 

 of mammalian tissues should aid the student to grasp functional 

 anatomy, for the cell is the unit of structure and of function. 

 Groups of cells of the same kind form a tissue ; two or more tissues 

 form an organ, or functional unit such as a muscle with its parts 

 and attachments; and the necessary organs form the organism. 



There are five kinds of elementary (primary) tissues: Con- 

 nective, epithelial, muscular, nervous, and fluid or circulat- 

 ing tissues. The first four are often referred to as fixed tissues, 

 and some histologists do not accord the fluid tissues (blood and 

 lymph) the rank of an elementary tissue (chiefly because the 

 cell elements, the corpuscles, are independent of each other and 

 are suspended in a fluid medium) , but place them in the group 

 of connective tissues with which they develop from the mesen- 

 chyme of the mesoderm, which, as its name implies, is the 

 middle one of the three blastodermic layers of early embryonic 

 stages and which also gives rise to the muscles. 



Prepared slides of mammaHan tissues belonging to the five 

 elementary groups will be furnished for this study. At this 

 time the instructor should explain briefly the process of fixing, 

 dehydrating, infiltrating, and cutting the tissues into sections 

 about S}JL (0.008 mm.) thick; how these thin sections are fastened 

 to the 1X3 inch glass slip, stained, dehydrated, and covered 

 with a very thin slip of glass, dried and made ready for class use. 



In studying the cellular structure of tissues with the com- 

 pound microscope, the student should always locate the struc- 

 tures he wishes to study with the low power (16 mm.) objective 

 before turning the high power (4 mm.) objective onto the object 

 to study the finer structure. It is a good plan to be certain 



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