62 STUDENTS HISTOLOGY 



After washing, and while yet in the water, expose to sunlight 

 (perhaps fifteen minutes) until a brown tint is acquired, which 

 indicates the proper staining. 



The mesentery has been left connected with the intestine, so 

 that the former might not curl. The preparation having been 

 dehydrated with alcohol, and having reached the oil of cloves, pro- 

 ceed with a pair of scissors to snip off a small, flat piece of mesen- 

 tery. Remove it to a slide and mount in balsam. The omen turn 

 of a rabbit, cat, or dog may be prepared in a similar manner. 



The outlines of the endothelial cells appear as dark lines where 

 the silver has stained the cement-substance. These lines are often 

 tortuous and serrated. The nuclei are not seen, unless they have 

 been separately stained with carmine or some other nuclear dye. 



Openings called stomata occur on the serous surfaces, which 

 connect the cavities with underlying lymphatic vessels. The 

 stomata occur at the points where several endothelial cells meet. 

 The opening is sometimes surrounded by several small, granular 

 cells, called "guard cells." Changes in the size of these cells 

 modify the size of the stomata. 



CONNECTIVE TISSUES 



Certain elementary structures of similar origin and mode of 

 development, and serving alike to unite the various parts of the 

 body, have been termed connective tissues. Custom has restricted 

 the term, in its everyday employment, so as to apply to white 

 fibrous tissue, or, at least, to tissue which always resembles this 

 more closely than any other. 



WHITE FIBROUS TISSUE 



This, the connective tissue par excellence, is composed of exceed- 

 ingly fine fibrillse (only 0.6 /* in diameter), which are aggregated in 

 irregularly sized and variously disposed bundles. It forms long 

 and exceedingly strong tendons connecting muscle and bone; its 

 fibers interlace, forming the delicate network of areolar tissue; it 

 forms thin sheets of protecting and connecting aponeuroses ; or, 

 supporting vessels, it permeates organs and sustains the paren- 

 chyma of glands. 



The fibers are held together by means of a transparent cement, 



