772 DIRECTIONS FOB LABORATORY WORK 



VI. CONNECTIVE TISSUE 



(A) FIBEOUS VARIETIES (or connective tissue proper). These de- 

 velop from the middle germ layer (mesoderm). 



(1) EMBRYONAL. Study the subcutaneous tissue in a stained trans- 

 verse section of a 10 to 20 mm. pig embryo. Note differences in 

 appearance of deeper and more superficial regions, representing earlier 

 and later stages in the histogenesis. Draw (53 a and b) small area from 

 each of the two regions. Note the shape of the cells, and the character 

 and quantity of the intercellular substance. Is embryonic connective 

 tissue (mesenchyma) composed of discrete cells or does it correspond to 

 a syncytium? Does the matrix contain fibrils? 



(2) Mucous (Gelatinous). This type is found typically only in 

 the umbilical cord, where it is known as the jelly of Wharton. The 

 vitreous humor of the eye is also comparable to mucous connective tissue. 

 In a stained section of the umbilical cord study a region, some distance 

 removed from the large central blood vessels, and note the various forms 

 of cells; and the character and quantity of the intercellular substance 

 (matrix), including the fibrils. Draw (54) a small area. Is mucous 

 connective tissue syncytial in character? Is it vascularized ? Define 

 'fibroglia.' 



(3) RETICULAR (Retiform). This forms the supporting frame- 

 work for the cells (lymphocytes) in lymphoid tissue. Select for study 

 a thinner region of stained section of some lymphatic organ (e.g., hemal 

 node, lymph node, spleen) where the lymphocytes are sparse. Draw 

 (55) a small area, noting the character of the fibril bundles, and their 

 relation to the lymphocytes and to certain stellate connective tissue cells. 

 Do the bundles anastomose? (A demonstration preparation of the retic- 

 ulum of a lymph node or of the spleen, from which the lymphocytes have 

 been removed by 'digestion', or by shaking, or by washing in warm water 

 after gelatin injection and freezing Mall's technic may be substituted 

 to advantage for this exercise.) 



(4) AREOLAR (Loose fibro-elastic). This type includes fibro-elastic 

 structures of greatly varying densities. Spread out taut on slide 

 a thin film of fresh subcutaneous or intermuscular tissue of some mam- 

 mal (e.g., guinea pig, rabbit, rat). Allow the ends to dry fast to the 

 slide, keeping the center moist with physiologic salt solution. Mount 

 under cover-glass and examine the several types of fibers. Note the dull, 

 white, wavy bundles of collagen fibrils, and the clear, shiny, stouter elas- 



