REGENERATION AND DEATH 201 



mander may regenerate its lost tail. By the growth 

 of nerve fibres a whole nerve may be regenerated, a 

 fact which is often of the utmost practical medical and 

 surgical importance. Many researches upon the re- 

 generation of nerves have been made, and some 

 questions about it are still subject to dispute, but I 

 have confined myself to such statements as seem to 

 me beyond controversy. 



Our next picture demonstrates a similar phenom- 

 enon. It represents muscle fibres which have been 

 injured. Every muscle fibre contains in its interior 

 its contractile substance, the fibrils, in regard to which 

 I have already spoken to you ; but it also contains a 

 certain amount of substance which is still undiffer- 

 entiated protoplasm. Now when a muscle fibre of 

 this sort is injured, we find that the muscular struc- 

 ture, properly so-called, will in many cases quite 

 disappear, but then the protoplasmic material, which 

 is the undifferentiated substance, will begin to grow 

 and the nuclei will begin to multiply, a, b. This may 

 happen at the end of a muscle fibre e, f- producing 

 there a considerable mass of protoplasm, with nuclei 

 multiplying in it ; or we may find a chain of nuclei, 

 each with its separate protoplasmic body, b ; such 

 nuclei will multiply. When the increase of the un- 

 differentiated protoplasm has gone on far enough, the 

 injured muscle will produce again the muscular sub- 

 stance proper the contractile fibrils. Muscular fibre, 

 in other words, can be regenerated by itself, but only 

 by the growth of its undifferentiated portion ; the 



