Protoplasmic Streaming — Relation to Gel Structure 151 



are (1) an increase, up to about 10 per cent, in the height of the 

 spike potential, (2) an increase, up to 20 per cent, in the duration 

 of this potential, and (3) an increase, up to 12 per cent, in the rate 

 at which the action potential is propagated. At pressures above 

 6,000 lbs. the height of the spike and the rate of propagation fall 

 away, and at about 13,000 lbs. the nerve becomes practically non- 

 responsive. However, the duration of the potential continues to 

 increase throughout the higher range. At pressures above 5,000 lbs. 

 it is also observed that a single short shock evokes not one, but 

 several (up to four) , discharges, even in the single fibre. 



C. THE MOTILITY OF CILIA AND FLAGELLA 



The work of Pease and Kitching ('39), on the influence of pres- 

 sure on ciliary frequency in the gill filaments of the common mussel, 

 Mytilus edulis, clearly demonstrates the accelerating effect of sudden 

 increases in the pressure level, and the deceleration which occurs 

 with each abrupt drop of pressure (see Fig. 10) . In these experiments 

 a stroboscopic method, accurate to the nearest 10 beats per minute, 

 was used to measure the frequency of the ciliary beat. 



It is interesting to note that, at least for moderate changes of 

 compression, the frequency tends to return to the initial basic value, 

 when the pressure is maintained at the higher or the lower level. 

 When pressures above 5,000 Ibs./in.- are maintained, however, after 

 the initial burst of activity, the basic rate falls away rapidly, and 

 within 10-15 minutes the cilia stop — an observation which is in 

 agreement with the earlier studies of Regnard ('84 and '91) and of 

 Certes ('84). 



Pease and Kitching find no parallel between the changes of fre- 

 quency and the known effects of pressure upon protoplasmic gel 

 systems. They do, however, point out the striking similarity between 

 the ciliary frequency effects and the cardiac frequency results 

 obtained by Edwards and Cattell ('28). 



Quantitative studies dealing with pressure effects on the motility 

 of flagella are entirely lacking, and the qualitative observations 

 which have been made are very fragmentary. However, it seems 

 safe to say that this type of movement is even less susceptible than 

 the ciliary type to inhibition by pressures within the range of 

 reversible action. For example, Marsland and Brown observed in a 

 cinematographic record of the action of pressure upon amoeboid 

 movement that the motility of a few small flagellates, which inad- 



