20 LORD ROTHSCHILD 



whom the results will be published, the changes with time in the 

 concentrations of ATP, ADP, and AMP + IMP in anaerobic bull 

 spermatozoa have been measured. The anaerobic heat production 

 and impedance change frequency were measured at the same time. 

 Large and characteristic changes occur in the rate of heat production 

 of anaerobic bull spermatozoa without any corresponding changes in 

 nucleotide concentration, and the same applies if one compares them 

 with impedance change frequency. A further point of possible in- 

 terest is the high concentration of ADP in comparison with that 

 of ATP. This is characteristic not only of anaerobic bull spermatozoa 

 but also of just ejaculated spermotozoa. Can someone say, for cer- 

 tain, whether bull spermatozoa are anaerobic or aerobic before 

 ejaculation? 



The heat production of anaerobic bull spermotozoa is caused by 

 the combustion of fructose to lactic acid and the partial neutraliza- 

 tion of the lactic acid by the seminal plasma. Useful work associated 

 with this reaction is ultimately degraded to heat by the tails of the 

 spermatozoa. As mentioned earlier, the amount of energy upon which 

 the spermatozoa can, ideally, draw for movement is the free energy 

 change, not the enthalpy change, associated with the reaction. The 

 two values are very different, the former being 47.3 kcal/mole, and 

 the latter 27.7 kcal/mole. 



RHEOTAXIS 



A different aspect of sperm movement which has recently in- 

 trigued me and which I believe may throw some light on the mecha 

 nism of sperm movement concerns the idea, often asserted in the 

 nineteenth century, that spermatozoa swim upstream. Upstream is, 

 of course, a vague phrase, about which I shall be more precise a little 

 later. Walton believed at one time (1952) that these nineteenth cen- 

 tury assertions were based on errors of observation and, perhaps, on 

 wishful thinking, it being thought that because eggs came "down" 

 the oviduct, there must be a flow of fluid down it and that spermato- 

 zoa would not reach the eggs in time unless they had swum upstream. 

 In tackling this problem, the first task is to devise a controllable 

 method of flowing a sperm suspension along a container and to be 

 able to characterize the velocity gradient. The best system is one 

 similar to a Couette viscometer, with the velocity gradient in the 



