RHYTHMIC PULSATION 



315 



shorter length than that of the other 'normaF pieces, i.e., cloacae 

 cut off below the level a a (fig. 1). It is possibly of signifi- 

 cance that the earlier part of these exhaustion curves bears a 

 superficial similarity to those of autocatalytic reactions, which 

 might be taken to indicate that there is here an autocatalyst of 

 exhaustion, represented by fatigue products. The sharp upward 



100 2O0 v500 400 500 lOOO 



Duration of pulsations in minutes 



bend of the curves near the time of cessation of pulsation indi- 

 cates that pulsation continues until some critical condition is 

 arrived at within the pulsating mechanism, beyond which spon- 

 taneous rhythm is not possible. The exhausted condition was 



