50 THE CONNECTIVE TISSUES 



to the loose fibroelastic type often make it difficult to differentiate. 

 The appearance of the reticular cells may be studied in routine 

 preparations of lymph glands of mammals. In the central portion 

 of such a gland there is a diffuse arrangement of tissue and a net- 

 work of reticular cells may be observed forming a support for the 

 lymphocytes. 



LOOSELY ORGANIZED FIBROELASTIC TISSUE. 



This is probably the most widely distributed type of connective 

 tissue and also contains the component elements to be found in other 

 types. It is well exemplified by subcutaneous tissue W'hich is easily 

 accessible for study. When the skin is removed from a freshly 

 killed mammal, a moist, white, filmy tissue is seen lining the under- 

 surface of the skin. It tears easily as the skin is removed; part 

 remains attached to the skin and part adheres to the underlying 

 tissues of the body. It has been called areolar tissue because open 

 spaces may be seen among the fibrous intercellular elements when 

 spread out on a slide. In the normal state of the tissue, however, 

 these spaces are filled with a tissue juice, or ground substance, so 

 that it is advisable to use the longer, more descriptive term instead 

 of the term areolar which is misleading. Study of this tissue 

 clearly reveals cells and fibers, but the ground substance or tissue 

 juice noted by the feeling of moisture in the fresh tissue, is difficult 

 to demonstrate in preparations. 



Cell Types. — Cells are not easily seen in fresh tissue mounts, nor 

 is it easy to demonstrate all the types in any one preparation. 

 They are often studied by means of intravitam staining, a process 

 in which small amounts of harmless dyes, such as neutral red, are 

 introduced subcutaneously in a living animal, and, later, a small 

 amount of the subcutaneous tissue is carefully removed for study. 

 In such cases, certain cells take up the dyes in a characteristic 

 fashion. 



Fibrocytes. ^Verived directly from mesenchyme, these cells 

 become larger, elongated, and flattened. They have long cyto- 

 plasmic processes and in edge views or sections they appear spindle- 

 or rod-shaped. The cytoplasm is clear and stains only faintly with 

 acid dyes, thus making the cell outline indistinct in preparations. 

 The nucleus is relatively large and oval and appears lightly stained. 

 A nucleolus is usually present. In some ])re])arations furrows 

 appear on the surface of the cells presumably as a result of their 

 close association with fibers. Early investigators concluded that 



