BIOLOGY OF SPERMATOZOA 



729 



permits long-term storage and, in the long 

 i-un. greater use of the sperm. An additional 

 advantage is that the storage intervals al- 

 low for i)rogeny testing, a procedure which 

 takes time and is of considerable importance 

 in identifying the breeding value. As applied 

 to man, on the other hand, the method would 

 seem to have only limited usefulness in ex- 

 (■e|)tional instances. One might suppose, for 

 example, that successive ejaculates of an 

 ()lig()s|)erniic individual could be stored and 

 pooled in this fasliion and give, upon insemi- 

 nation, a sufficiently high sperm count to 

 insure fertilization. The advantage of trans- 

 portability of frozen semen, i)ractical in ani- 

 mal husl)andry, would not be expected to 

 play a significant role in matters concerning 

 human fertility. 



'The changes which may occur in cells 

 during storage at such low temperatures, or 

 during the freezing or thawing process, can 

 only be surmised. Based on the resumption 

 of motility at room temperature and ferti- 

 lizing cajjacity, the alterations in bull sper- 

 matozoa must be minor. In other kinds of 

 spermatozoa, those of the rabbit for exam- 

 ple, metabolic and permeability changes 

 may l)e more pronounced. Subtle changes, 

 sucli as might be induced in the cytogenetic 

 api)aratus, are unknown; there is the ques- 

 tion of whether they have been sought. 



The mechanism of the protective action 

 of glycerol in maintaining the spermatozoa 

 during the relatively slow freezing process 

 and while in storage is obscure. The effect 

 is probably not merely one of the prevention 

 I if ice crystal formation, but rather one 

 which involves the stability of the internal 

 ionic concentration of the cell. One can sup- 

 pose that without glycerol, the withdraw^al 

 of fi-ee water would result in severe changes 

 possibly involving an increase in ionic 

 strength, alteration in jiH, the production 

 of toxic concentrations of such substances 

 as urea and dissolved gases, and an actual 

 liliysical I'eorganization of intracellular 

 components (Lovelock, 1957). One sugges- 

 tion is that the elements sensitive to deep 

 fieezing are lii)oprotein complexes which, in 

 the ])resence of glycerol, aic pic\-ented fi'oni 

 • lenaturation (Lovelock, 1907). 



Although deep freezing and cold storage 

 of sperm are currently receiving the great- 

 est attention, othei- methods of controlling 



metabolism and motility are being consid- 

 ered and may ultimately prove useful in the 

 preservation of sperm for artificial insemi- 

 nation. Such metabolic blocking agents as 

 tetrazolium compounds (Bishop and Math- 

 ews, 1952b) and carbon dioxide (Salisbury 

 and VanDemark, 1957; VanDemark and 

 Sharma, 1957; du Mesnil du Buisson and 

 Dauzier, 1958) can reversibly inhibit the 

 processes involved in the utilization of sub- 

 strate and the expenditure of energy. An- 

 other api)roach has recently been suggested 

 by the work of Petersen and Nordlund 

 ( 1958) whose })reliminary experiments in- 

 dicate that bull sperm can be subjected to 

 150 atmospheres of pressure, in nitrogen, 

 and sur\-i\-e such treatment for two weeks, 

 after which motility is regained. Whether 

 such a procedure destroys fertilizing capac- 

 ity has not yet been ascertained. 



V. Sperm Transport and Survival in the 

 Female Tract 



The vigorous motility of seminal sper- 

 matozoa has long been a source of fascina- 

 tion and naturally gave strong support to 

 early suppositions that migration in the fe- 

 male tract is due to the activity of the cells 

 themselves. This is now known not to be 

 generally true, and only in certain limited 

 segments does active sperm motility seem 

 of possible importance in transport from the 

 vagina to the site of fertilization in the ovi- 

 duct. Suggestions have been made, in fact, 

 that sperm motility may be unnecessary 

 even for egg penetration (Allen and Grigg, 

 1957) , but such has never been demonstrated 

 in studies of fertilization of either inverte- 

 brate or vertebrate gametes. 



The over-all transport system for mam- 

 malian spermatozoa is principally provided 

 by muscular contractions of the walls of the 

 tract, with a questionable role played by 

 ciliary activity of the mucosa; under some 

 circumstances, however, active flagellation 

 of the gametes themseh^es is important (cf. 

 Hartman. 1939). 



A. DUR.\TION OF TRANSPORT 



The most striking evidence that sperm mi- 

 gration in the female tract cannot be attrib- 

 uted solely to sperm motility is afforded by 

 the results of studies of the rate of transport 

 and the time required to pass from the point 



