ISO REGENERATION 



according to Ribbert, if pieces of such organs are composed of 

 epithelium only, they cannot be successfully grafted. For instance, 

 the cells of the cornea can be readily separated from their under- 

 lying connective tissue, and can be kept alive in the lymph gland, 

 but the cells diminish in number, show retrogressive metamorphosis 

 in the direction of atrophy, and are finally absorbed. It seems that 

 epithelium by itself cannot extract nourishment from its surround- 

 ings. Nothing is easier, however, than to transplant epithelium, 

 if its connective tissue is present. The connective tissue furnishes 

 so good a basis for nourishment that the epithelium not only lives, 

 but may continue to proliferate. Ribbert finds that pieces of skin 

 roll in after their removal. Then a process of growth takes place 

 corresponding to that which follows a wound in the skin. The 

 surface is closed and a small cyst is formed with a central cavity. 

 The epithelium undergoes no changes during the first days or weeks. 

 It remains stratified and shows an active process of cornification and 

 desquamation. Similar results were obtained when pieces of the 

 conjunctiva were transplanted, either under the skin in the anterior 

 chamber of the eye, or in the lymph gland. 



A small piece of the lining epithelium of the trachea with its 

 underlying cartilage was also placed in the lymph gland. The epi- 

 thelium grew, and covered over the wounded surface, forming over it 

 only a single layer of cells. The old many-layered epithelium also 

 became arranged in a single layer. 



The wax glands, found in the inguinal folds of the rabbit, were 

 also transplanted. The gland is composed of closed, compressed 

 alveoli, surrounded by large, polygonal, clear cells. Small pieces of 

 a gland, transplanted upon the lymph gland, underwent character- 

 istic changes. The cells of the alveoli were changed into a stratified 

 epithelium ; and broken-down cells, and wax, were found in the interior 

 of the alveoli. The central alveoli underwent the greatest change, 

 while some of the peripheral alveoli that were in contact with the 

 lymph gland remained unchanged. It seems that the difference is due 

 to the better nourishment of the outer alveoli. After several months 

 the alveoli swell up and degenerate. Transplanted pieces of the 

 salivary glands also change, the alveoli producing a lining epithelium 

 like that of the transplanted wax gland. The same change was ob- 

 served in a piece of a salivary gland transplanted in the body cavity. 



Small pieces of the liver were cut off and placed in the lymph 

 gland. They did not always grow as well as did the preceding 

 tissues, but often went to pieces. If they healed, the liver tissue 

 often remained unchanged for several weeks. After two or three 

 weeks connective tissue appeared between the peripheral liver cells, 

 separating the cells from each other. The cells grew smaller, their 



