1 1 2 XEGENERA TION 



. 



lobules, tubes, etc., the process is spoken of as one of hypertrophy 

 rather than of regeneration. 



Kretz found a case in which the entire parenchyma of the liver 

 seemed to have been destroyed, presumably by a poison from some 

 micro-organism, and later a regeneration of the tissue had taken 

 place. If this conclusion is correct, it shows that sometimes an in- 

 ternal organ may meet with an injury that does not directly destroy 

 the rest of the body, and the animal may survive. 



The regeneration of the salivary gland of the rabbit described by 

 Ribbert is another example of an internal organ that can seldom be 

 injured, and yet can be replaced after artificial removal. Weismann 

 ('93) has recorded an experiment in which half of a lung of triton 

 was cut off. After fourteen months the lung had not been restored 

 in four individuals, and in one " it was doubtful whether a growth of 

 the lung had not taken place, but even in this case it had not recov- 

 ered its long, pointed form." 



The regeneration of the eye in triton was first made known by 

 Bonnet. The right eye was partly cut out, and after two months it had 

 completely regenerated. Blumenbach, in 1784, removed the anterior 

 part of the bulb of the eye of " Lacerta lacustris." Six months later 

 a smaller bulb was present. Phillipeaux (*8o) found that if the eye 

 of an aquatic salamander was not entirely removed, a new eye regener- 

 ated ; but if the eye was completely extirpated a new eye did not 

 appear. Colucci, in 1885, described the regeneration of the lens of 

 the eye of triton from the edge of the optic cup. Wolff, later, inde- 

 pendently, discovered the same fact, and it has been more recently 

 confirmed by E. Miiller ('96), W. Kochs ('97), P. Rothig ('98), and 

 Alfred Fischel ('98). The most important part of this discovery is 

 that the new lens develops from the margin of the optic cup, and not 

 from the outer ectoderm, as it does in the embryo. This result will 

 be more fully discussed in a later chapter. It is highly probable in 

 this case that the regeneration stands in no connection whatsoever 

 with the liability of the eye to injury, for of the large number of 

 salamanders that have been examined, none has been found with 

 the eye mutilated. The position of the eye is such that it is well 

 protected from external injury, and the tough cornea covering its 

 outer surface would also further protect it from accidental injury. 

 When we recall the high degree of structural complexity of the eye, 

 its capacity to regenerate, if only a portion of the bulb is left, and its 

 powet to replace the lens if this is removed are certainly very remark- 

 able facts. We find here, I think, an excellent refutation of the 

 incorrectness of the general assumption of a connection between 

 regeneration and liability to injury. Moreover, since there is no 

 evidence whatsoever to show that the eyes in these animals 'ire ever 



