Il8 THE GERM-PLASM 



afterwards killed. An examination showed that the right lung 

 had not become restored : it was only half as long as the left one, 

 and its end was blunt, and not pointed as in the normal lung. 

 Four other similar experiments yielded like results : in one of 

 these it was doubtful whether a growth of the lung had not taken 

 place, but even in this case it had not recovered its long, pointed 

 form. 



These experiments are still being continued, but we may 

 already deduce from them that a striking disproportion exists 

 between the regenerative power of the external parts of a newt 

 and that of its lungs. This difference seems even more marked 

 if we bear in mind that in the case of a limb the process of 

 regeneration is a very complex one, for complicated parts, con- 

 sisting of many entirely different portions, have to be reproduced ; 

 whereas a lung is a simple hollow sac, which has no joints, and 

 the histological structure of which is relatively simple. 



We therefore infer that the internal parts, which are not ex- 

 posed to injuries of an ordinary kind, do not possess a greater 

 capacity for regeneration in these species than they do in the 

 highest Vertebrates, which are so exceptionally inferior to them 

 as regards the regenerative power of the external parts. Hence 

 there is no such thing as a general powe7' of regeneration : in each 

 kind of animal this power is graduated according to the need of 

 regeneration in the part under consideration : that is to say, the 

 degree in which it is present is mainly in proportion to the 

 liability of the part to injury. 



This conclusion is closely connected with the fact that the res- 

 toration of a part which possesses the power of regeneration in a 

 high degree, can only take place as the result of definite injuries 

 which are in a manner provided for, and not from a7iy kind of 

 injury. Philippeaux was the first to discover that the limb of a 

 Triton does not o;row again when it has been removed at the 

 joint, and that, in fact, it only does so when it is cut or torn off, 

 so that the bone is injured. This fact has been explained by 

 referring it to the law of the specific nature of the tissues, accord- 

 ing to which bone can onlv be formed from bone, and the bone 

 of the limb must be injured before it can become capable of 

 being formed anew. It seems to me that this explanation is 

 insufficient, although it is founded on a correct principle, accord- 

 ing to which the injury to the bone causes the stimulus by which 

 the cells of the stump are incited to proliferate. This is certainly 



