PHYSIOLOGY OF REGENERATION 15 



proceeds. The detrimental influence of the extra injury is spe- 

 cially strong during the first few days following the operation, 

 owing probably to the fact that a greater claim is then made upon 

 the organism's reserve formative energy; but if the new tail has 

 already got a sufficient start in regeneration its further progress 

 can not be impeded by an additional mutilation of the organism. 



B. RELATION BETWEEN FREQUENCY OF INJURY AND RATE OF 



REGENERATION 



Next in importance to the problem of the relation between the 

 rate of regeneration and degree of injury stands the problem of 

 its relation to the frequency of injury. In earlier studies (Morgu- 

 lis, '08) I have shown that the regenerative rate decreases 

 with each repeated operation. Similar conditions were also 

 observed in Podarke ('09b), although it was there pointed out that 

 the worms tend to regain their original rate of regeneration. The 

 inference of real importance to be drawn from those experiments 

 is that within a given period of time an organism generates more 

 tissue the more often it has been operated upon. In 1908 Zeleny 

 suggested that after successive operations the rate of regeneration 

 increases, but his data at that time were quite inconclusive. 

 Lately ('09a) he has brought forth additional evidence, obtained 

 with great precaution against any possibility of error, and that 

 investigation has led him to formulate his opinion more care- 

 fully, as follows: "The data as a whole make it highly probable 

 that the pure effect of successive removal is either no change in 

 rate of regeneration or an increase in rate" ('09a, p. 508) 



I performed a few experiments on Podarke to verify my former 

 observation that the rate of regeneration decreases after repeated 

 mutilations, and in what follows I shall present the outcome of 

 those experiments. It should be recalled that in experimenting 

 with worms one does not encounter such perplexing difficulties 

 in the way of controlling conditions as the Crustacea, for instance, 

 offer. Other factors, too, are easily controllable. The experi- 

 ment consisted simply in allowing some worms to regenerate 

 continuously for several weeks, while on other worms from the 



