200 AGE, GROWTH, AND DEATH 



threads ; its protoplasmic body is large, and some- 

 thing of its structure I have told you in a previous 

 lecture. A German investigator, Professor Gruber, 

 has succeeded in dividing one of these Sten- 

 tors, a unicellular creature, animalcule, common in 

 fresh water, into three parts, in such a method of 

 cutting as is illustrated by the figure on the left. 

 Each of the three parts restored itself and became a 

 complete Stentor. In such experiments the proto- 

 plasm around the nucleus begins to grow ; gradually 

 the original form is again assumed ; the creature 

 grows larger and larger, until each piece acquires 

 the parent size, and, so far as we can see with 

 the ordinary microscopic examination, identically the 

 parental structure. That which was lost has been 

 regenerated. We learn, then, that regeneration is 

 a faculty which a single cell, a single unit, may 

 possess. 



Another example of unicellular regeneration is of- 

 fered us by nerve fibres. A nerve fibre is a thread- 

 like prolongation of a nerve cell (neurone) and is of 

 course a part of the cell, as much so as the proto- 

 plasmic body immediately surrounding the nucleus. 

 When a nerve is cut across, as happens, for instance, 

 necessarily in every surgical operation, the nerve fi- 

 bres are severed. The part which is separated from 

 the central cell dies by a degenerative process, the 

 part which is connected with the cell, on the contrary, 

 may grow and elongate itself. In other words, the 

 cell regenerates the part which it lost, just as a sala- 



