i88 



FINE-STRUCTURE OF PROTOPLASM 



II 



Fig. 

 shows 



40 44 

 Time in minutes 



Fig. 109. Electrical record and mechanical record of streaming 

 Physarum cytoplasm (from Kamiya and Abe, 1950). 



This shows that the plasmic flow of slime moulds is a polyrhythmic 

 movement caused by numerous sine-like contractions of various 



periods. 



109 (below) 

 the oscilla- 

 tions of the pressure 

 in a Plasmodium 

 strand of Physarum. 

 There are cyclic 

 changes of the amp- 

 litudes and a sys- 

 tematic displacement 

 of the central point 

 between maximum 

 and minimum press- 

 ures. This means 

 that there is a more 

 intense flow in one 

 direction of the 

 strand than in the other, with the result that the cytoplasm moves 

 slowly in the direction of lower pressure. 



Kamiya and Abe (1950) have also measured the electric potential 

 difference between the two poles of a PljsaniM strand with its oscil- 

 lating plasmic flow. It changes in a similar way to the internal pressure, 

 showing sine waves with the same periods and corresponding am- 

 plitudes within 10 mV, but there is a small phase difference. The maxi- 

 mum and minimum values of the electrical record lag behind those of 

 the mechanical record by about half a minute, indicating that the con- 

 traction involving a pressure change is not caused by the measured 

 potential differences. The pressure oscillations can be eliminated by 

 appropriate counterpressures. Then the rhythmic potential changes 

 go on. This means that the chemical processes causing contraction 

 operate even if the contraction is impeded. 



These details of rhythmic contraction are reminiscent of muscle 

 activity, which is due to the contractility of actomyosin (see p. 358). 

 It is therefore likely that protoplasmic flow is also maintained by 

 contractile proteins in the cytoplasm. These can only develop their 

 full activity in the gelated state. It would seem that these statements 



