REGENERATION OF INTERNAL ORGANS 113 



subject to diseases caused by bacteria, and much evidence to show that 

 they are not so injured, we are still further confirmed in our general 

 conclusion. 



It has been known for a long time that even in man the lens of 

 the eye is sometimes regenerated after its removal. The regeneration 

 has been supposed to take place from the old capsule of the lens, or 

 possibly from a piece of the lens left after the operation ; but what- 

 ever its origin, the fact of its regeneration in man, and in other mam- 

 mals also, is a point of some interest in this connection. 



Podwyssozki ('86) found that regeneration may take place in the 

 kidney of certain mammals, best in the rat, more slowly in the rabbit. 

 The restoration of the lost part takes place first by replacement of 

 the epithelium. The old canals may then push out into the connec- 

 tive tissue that accumulates in the new part, but there is no new for- 

 mation of canals or of glomeruli. According to Podwyssozki the 

 regeneration of the kidney is less complete than that of any other 

 gland. Peipers has reinvestigated the subject, and his results agree 

 in the main with those just given. He finds in addition that new 

 canals may grow out from the old ones into the new part. 



Podwyssozki and Ribbert ('97) have found that the salivary gland 

 has a remarkable power of regeneration. Ribbert removed a half 

 (or even more than this) of the salivary gland of the rabbit. In the 

 course of two or three weeks new material had developed over the 

 cut-surface. In one case at least five-sixths of the gland had been 

 taken out, and at the end of three weeks the gland had regenerated 

 to its full size. Microscopic examination showed that the greater 

 part of the gland was made up of new lobes, some of which were as 

 large as, others smaller than, the normal lobes. The new part con- 

 tained new tubes with terminal acini. These had arisen from the 

 tubes of the old part. The connective tissue of the new part also 

 came from that of the old. In this case a true process of regenera- 

 tion takes place from the cut-surface ; in addition a certain amount of 

 enlargement, or hypertrophy, also takes place in the old part. Rib- 

 bert believes there is a connection between the process of hypertrophy 

 and of regeneration of such a kind that the more active the one, the 

 less active the other. 



Regenerative changes are known to occur in other internal organs 

 besides these glandular ones. Broken bones are united, if brought in 

 contact, by a process that involves a certain amount of regeneration. 

 Although new bony tissue may be formed at the region of union, the 

 bones of mammals and of birds do not seem able to complete them- 

 selves, if a part is removed, except to a limited extent. While the 

 broken bones of the leg or of the arm have the power of reuniting if 

 held for some time in place, yet in nature this condition can seldom 



