262 DAVID W. BISHOP 



a plasticizing action similar to that of muscle relaxing factor. This 

 component is not washed out during extraction or lost during storage 

 as seems to be the case with Kinoshita's relaxing factor of invertebrate 

 sperm. It is unlikely that this agent is adenylatekinase (myokinase) 

 since the latter activity is lost during prolonged extraction and storage 

 of mammalian spermatozoa. 



Two further physical characteristics of the model system may be 

 noted. Reactivated sperm can flagellate against an imposing viscous 

 stress exerted by an increase in the viscosity of the surrounding me- 

 dium (Bishop and Hoffmann-Berling, 1959; Brokaw, this symposium). 

 Attempts to assess the capacity of mammalian sperm models to ex- 

 ert a "maximal tension" equivalent to that of living cells were only 

 partially successful; nevertheless, the experiments did demonstrate 

 that mechanical work can be done by the reactivated cells against 

 an increased external force. 



Isolated flagella and fragments of the tails of mammalian sperm 

 models were prepared and tested for reactivation ability. Only intact 

 tails responded to ATP; distal fragments, even large segments, failed 

 to respond (Bishop and Hoffmann-Berling, 1959). This finding would 

 seem to support the view that the basal body and perhaps even the 

 mitochondrial region of the flagellum are essential for induced move- 

 ment, indicative of a whiplash type of process. The response of indi- 

 vidual segments of the intact flagellum, however, suggests that cutting 

 the tail into fragments severs long-chain constituents or filaments 

 necessary for shortening, similar to the cutting of an origin or in- 

 sertion of a muscle fiber. 



What bearing have such findings on the problem of the mechanism 

 of sperm movement? Interpreted in terms of muscle biochemistry, 

 some light is shed upon the contractile protein nature of the system, 

 on its nucleotide and cationic dependence, on the operation of an 

 oscillating process rather than on independent and discrete contrac- 

 tion and relaxation events. But beyond that, the use of the model 

 system as an experimental tool also affords an insight into associated 

 phenomena of flagellation at a cellular or physiological level. By the 

 very isolation of the functional wave-forming system, other aspects of 

 normal motility which are altered or abrogated by the extraction 

 process are more clearly delineated or set apart. 



