GRAFTING AND REGENERATION l8l 



protoplasm disappeared, and they at last disintegrated. Pieces of 

 the gall duct behaved differently. They sometimes showed active 

 growth, leading to the development of numerous branched canals. 1 



Pieces of the kidney, when transplanted, suffered a great change, 

 and were subsequently absorbed. Transplanted pieces of a testis 

 also changed. After six days, Sertoli's cells and the spermatozoa 

 disappeared. A kind of indifferent cell remained, characterized by 

 clear protoplasm and by a large nucleus. After seventeen days 

 further changes were observed, and later the pieces were com- 

 pletely absorbed. Pieces of the ovary rapidly disappeared, leaving 

 only a mass of interstitial connective tissue. 



The connective tissue underwent, in all the transplanted pieces, 

 characteristic changes. The tissue became less dense, the protoplasm 

 and nucleus of each cell enlarged. The cells multiplied, but only 

 very slowly. These changes took place after one or two days. After 

 a month or two the cells became more compact, their processes more 

 numerous, and the nucleus small and long. Later degeneration set in. 



Small pieces of bone from the caudal vertebrae were also trans- 

 planted, care being taken that each piece should contain some of the 

 periosteum and marrow. The bone tissue goes to pieces, but the 

 periosteum and marrow develop further. New bone is formed from 

 the cells of the marrow as well as from those of the periosteum. 

 Finally the entire piece, both its old and its new parts, is absorbed. 

 Pieces of muscles were also absorbed. 



These experiments of Ribbert show that transplanted pieces of 

 tissue do not increase in size by growth, but undergo changes 

 which he describes as a return to an earlier condition of develop- 

 ment. The abnormal condition of their existence seems to be the 

 cause of this change. The transformation may be due to a change 

 of nourishment, or to a loss of nerve influence, or to lessened func- 

 tional activity. 



These results have a direct bearing on the problem of regenera- 

 tion. They show that all kinds of tissue may continue to live, and 

 the cells multiply in different parts of the body, but there seems to 

 be nothing in these cases comparable to a regeneration of the entire 

 organ. In the new situation the cells often assume an entirely new 

 arrangement. After a period of activity, a process of degeneration 

 commences, and the piece atrophies. Ribbert thinks that the atrophy 

 is due to lack of nourishment, yet it is not clear how this could be 

 the case, since for the first few weeks after transplantation there is 

 an active growth, and in some cases, as in that of the bone, there is a 

 formation of new, characteristic tissue. It may be that the trans- 



1 It is known that the process of regeneration of the liver takes place especially from 

 the gall ducts. 



