166 MOVEMENT OF CILIA AND FLAGELLA 



Start of the '* effective stroke " by holding them at various distances 

 from the ciUary base. The mean torque around the base of these 

 ciUa found by this method w^as 3-9 x 10"*^ dyn cm in ciUa of 

 mean length 54*4 ju-. The variation in torque lay betw^een 

 2 X 10~' and 8 X 10~'^ dyn cm for cilia betv^een 42 ju, and 66 fju 

 in length at temperatures between 18 and 27°C. 



It has already been pointed out that these cilia are compound 

 structures, but it is not yet known how many component cilia 

 are involved. It is also important that these cilia show an 

 abnormal beat that deserves further study (p. 143). If the torque 

 measured were to be exerted throughout the effective phase of 

 beat, and the angle of beat is a little over 90°, the work done in 

 each effective stroke is about 8 X 10^'^ erg. The effective stroke 

 occupies nearly h sec, so that the compound cilium is doing 

 work at a rate of about 1*6 x 10~^ erg/sec in this phase of 

 beat. 



No attempt at calculation or measurement of the work done 

 against the internal resistance and stiffness of the cilium has yet 

 been successful. The energy available for use in locomotion of 

 bull sperm is some 10 times that required to overcome the external 

 resistance to movement of the sperm tail; it seems unlikely that 

 the work required to overcome internal resistance would use all 

 of the remaining energy that is available. 



It is interesting that flagella probably show a fairly uniform 

 expenditure of energy throughout their length, while cilia probably 

 use more energy in the effective stroke than in the recovery stroke, 

 and so most of the energy used by cilia goes to contraction of the 

 basal parts of the ciliary fibrils. Energy in convenient form may 

 be provided from mitochondria which usually lie near the bases 

 of cilia, or may also, it appears, be released nearer to the site of 

 utilisation. Sperm frequently carry mitochondria around the 

 neck (e.g. sea urchin) or the mid-piece (e.g. bull). While both 

 sea urchin and bull sperm may use energy at about the same rate 

 to overcome viscous resistance at their normal temperatures, the 

 bull sperm move at rather less than half the speed of the sea 

 urchin sperm, and have a much larger energy producing system 

 in their mitochondria. The bull sperm also has to move a larger 

 head through the fluid medium, and has to bend larger sheath 

 structures in the tail. 



