The Microscope. 245 



tissue, whilst the latter, quite like the leucocytes of the blood in 

 structure, pass in and out, becoming permanent only when repair of 

 the tissue is needed, to which process they contribute. 



A rather arbitrary classification of the connective tissues can be 

 made as follows: (1) fibrous tissue, (2) adipose tissue, (3) elastic 

 tissue, (4) retiform tissue, (5) adenoid or lymphoid tissue, (6) gela- 

 tinous tissue, (7) cartilage, (8) bone. 



Fibrous Tissue. — Select a small, spongy piece of subcutaneous 

 tissue, free from fat, place in the salt solution and, when carefully 

 teased out, cover and examine. Little wavy bundles of fibers will 

 be found. They do not branch nor communicate, and have no appar- 

 ent structure. The bundles do not run parallel, but cross and 

 recross, leaving little spaces or areolae — hence the name " areolar 

 tissue," sometimes applied to this form of fibrous tissue. The fibers 

 are held together by a homogeneous cement substance. In the 

 interstices of the bundles an occasional connective -tissue cell may be 

 discovered. It is generally flattened, branched, and contains a 

 nucleus. In the firmer bundles of tissue the cell may be so com- 

 pressed as to assume a spindle shape. 



Fibrous tissue seldom exists in a pure state. In the specimen 

 under examination a few fibers of another sort will be found. They 

 do not run in bundles, are not so wavy, are branched, connect with 

 each other, and curl at their detached ends. These are white elastic 

 fibers. 



Irrigate the specimen with dilute acetic acid. Whilst the elas- 

 tic tissue remains unchanged, the fibrous bundles swell up and 

 become transformed to a jelly-like substance. This swelling is some- 

 times accompanied by a curious phenomenon: the constriction of 

 the bundles at regular intervals by little bands. The cause is 

 unknown. It has been attributed to the twining of the cell -pro- 

 cesses, or of the elastic fibers, about the bundle, or that the bundle 

 possesses a sheath which has been destroyed by the acid, excepting 

 at the point of constriction. 



For the further study of fibrous tissue, examine the capsules of 

 the liver and kidney, prepared by the teasing process. The bundles 

 will be found loosely interwoven, and of coarser fiber. Examine 

 further the serous membranes. Cut out a small piece of a frog's 

 mesentery. Stain, if desired, in carmine or hematoxylin, wash in 

 weakly-acidulated (acetic acid) water, and mount in a drop of 

 glycerin. The fibers in the membrane run more parallel and are 

 arranged in lamellae. 



