386 BIOLOGY: GENERAL AND MEDICAL 



distance either among the older tubules or in the scar 

 tissue, but there is no new formation of glomerules, and 

 hence no true regeneration. When large portions of the 

 liver are removed by operation or destroyed by disease, 

 the remaining portions hypertrophy to carry on its func- 

 tion, and not infrequently offshoots from the bile ducts 

 are found extending some distance into the cicatrices, 

 as though new liver cell columns might form, but the 

 attempt seems to be abortive and to include only the 

 cells of the ducts and not those of the parenchyma. 

 The removal of the spleen is compensated for by enlarge- 

 ment of other lymphatic organs without any new for- 

 mation corresponding to the splenic structure. 



When a lung is removed or destroyed by disease, no 

 new tissue forms, though the entrance of an unusual 

 quantity of air may cause inflation of the undisturbed 

 tissue an injurious rather than a beneficial effect. 



The loss of the heart or the brain is certainly, though 

 not immediately, fatal. Life, however, is maintained 

 under these circumstances for a very short time only in 

 most cases. Destruction of the spinal cord results in 

 hopeless palsy. 



As the phylogenetic series is descended, the tenure of 

 life, after such mutilations, increases, and the ability 

 to repair damage becomes greater. Thus, in man, well 

 authenticated cases of regenerative changes in the eye 

 are rare, but in the triton a new lens is easily regenerated 

 and in some of the lower batrachia young individuals 

 may regenerate a whole eye. Still lower animals are 

 capable of regenerating the head, including the brain 

 and eyes, but the organs in such cases are simple and do 

 not form counterparts of the complex brains and eyes 

 of the vertebrates. When the heart is a simple con- 

 tractile tube slowly propelling the blood through vessels 

 not terminating in capillaries, the viscus may be dis- 

 pensed with for some time, during which a new one may 

 be provided, but when, as in the vertebrates, it is an 

 elaborately specialized pump with complexly arranged 



