180 REGENERATION 



from taking effect, and gives rise to a fore-limb field in the 

 regenerate. In this case the field is certainly not the immediate 

 continuation of that of the stump. Weiss (1927) amputated the 

 hand of a fore-limb, halved the lower arm longitudinally, and 

 removed one of the halves. He then covered the lateral wound 

 with skin, so that regeneration could not take place in this 

 region, but only at the distal transverse cut. A complete hand 

 was then formed by the regenerate on the halved lower-arm. 

 Here, again, the field of the regenerate could not be simply the 

 continuation of that of the stump. The opposite experiment can 

 also be made: if two limbs are made to grow together longitu- 

 dinally with their axes pointing in the same direction, and then 

 amputated, a single regenerate will develop in the common 

 wound (Swett, 1924). Polezajev (1936) went even farther, by 

 completely mincing the internal organs of the stump of an 

 amputated limb. Yet a more or less complete regeneration of 

 the limb was found to take place. If, however, the stump was 

 filled with minced tail tissue, tail-like regenerates were formed. 

 It follows that it is not necessary for the formation of a normal 

 organisation-field in the regenerate that the organs of the 

 stump should be in their normal positions. The field is clearly 

 not an extension of a pre-existing field in the stump, but it is 

 formed de novo in the regenerating tissue by an autonomous 

 process. The composition of the field is such that the organs 

 differentiating under its influence fit exactly onto those of the 

 stump. The following experiment proves that the nature of the 

 field is determined only by the level of the cut, and not by the 

 composition of the rest of the stump. Part of a limb, e.g. a 

 forearm, is isolated by means of two transverse cuts, one at 

 the elbow, and one at the wrist. It is then put back onto the 

 stump in an inverted position, so that the elbow is at the distal 

 end. Now at this end, a regenerate is formed consisting of the 

 parts that normally lie distally to this cut, i.e. forearm as 

 well as hand; a new forearm is consequently formed in the 

 regenerate, in spite of the fact that an (inverted) forearm is 

 present already. This must be due to the "elbow" qualities of 

 the wound in which regeneration takes place. 



Liosner and Woronzowa (e.g., 1937) have made a number of 



