722 



SPERM, OVA, AND PREGNANCY 



(Anderson, 1950). In conclusion, then, it 

 would seem that spermatozoa must develop 

 much of the machinery for movement 

 while undergoing spermiogenesis in the tes- 

 tis, that subtle changes occur while they 

 are in the mammalian epididymis such that 

 the full capacity for motility is here ac- 

 quired, and finally that this ability for 

 flagellation is realized normally only on 

 activation at the time of ejaculation. 



Although the problem has been recognized 

 for many years, only recently has serious 

 attention been paid to the nature of the pos- 

 sible changes in spermatozoa that are re- 

 sponsible for the acquisition of the capacity 

 for motility within the epididymis. In set- 

 ting forth a hypothesis to account for this 

 phenomenon, Salisbury (1956) has focused 

 needed attention on the problem. His sug- 

 gestion follows from determinations of cat- 

 ion concentration and freezing point de- 

 pression values of fluids of the genital tract 

 of the ram and the bull, noted above (Salis- 

 bury and Cragle, 1956). The supposition is 

 that a decrease in K+/Na+ and an abso- 

 lute increase in K+ -t- Na+ concentration, 

 nevertheless accompanied by a total reduc- 

 tion in tonicity of the fluids, bring about 

 permeability changes such that the sperm 

 become hydrated and, as a result, capable 

 of full metabolic activity (Salisbury, 1956). 

 An ingenious theory, it is, nevertheless, not 

 easily reconciled with the generally ac- 

 cepted demonstration that sperm lose water 

 rather than gain it as they mature (Lindahl 

 and Kihlstrom, 1952; IVIann, 1954). Until 

 more precise information is available con- 

 cerning such details as the sodium and po- 

 tassium concentrations of the sperm vis-a- 

 vis those of the fluid of the ducts, the actual 

 water- and cation-permeability of sperm at 

 various stages, and the effect of shifts in the 

 sodium-potassium ratio on motility of epi- 

 didymal sperm, in vitro, this problem cannot 

 be fully resolved. 



IV. Insemination 



At the time of mammalian sperm transfer, 

 many millions of vigorously motile sperma- 

 tozoa are introduced into the female genital 

 tract. Mixed with the fluid component of the 

 semen only at the moment of ejaculation, 

 the sperm normally are activated by their 

 sudden access to both oxvgen and the hex- 



ose energy substrate of the plasma. The 

 source and composition of the seminal fluid 

 have been reviewed elsewhere (Mann and 

 Lutwak-Mann, 1951 ; Mann, 1954) and are 

 further discussed in the chapter by Price 

 and Williams-Ashman. Only certain charac- 

 teristics of semen, relevant to sperm trans- 

 port and welfare, need be noted here. 



What is the normal function of seminal 

 plasma, and to what extent is it dispensable? 

 The fluid component contributed by the ac- 

 cessory glands can conceivably serve several 

 functions which include its role as (1) a 

 vehicle for sperm transport, (2) a medium 

 containing essential inorganic ions and of 

 adequate buffering capacity, (3) a satisfac- 

 tory osmotic milieu, and (4) a source of 

 energy substrate. Seminal plasma, by virtue 

 of its very complex composition, also per- 

 forms other duties. It supplies, for exam- 

 ple, the enzyme and substrate responsible 

 for vaginal-plug formation; it contains cer- 

 tain substances, unique to the reproductive 

 fluids, such as antagglutin which ostensi- 

 bly prevents undue sperm agglutination; it 

 provides such ingredients as ascorbic acid, 

 ergothioneine, and possibly glutathione, 

 which may play a role in the adjustment of 

 the oxidation-reduction potential. On the 

 other hand, some components of seminal 

 plasma may indeed be by-products with no 

 obvious beneficial role and even, perhaps, 

 with harmful effects on the gametes; both 

 alcohol and sulfonamides, for example, are 

 excreted into the plasma (Farrell, 1938; 

 Osenkoop and MacLeod, 1947). 



Since the vital process of sperm activation 

 is accomplished by their admixture with 

 plasma, and since a fluid vehicle is essential 

 for sperm transport, it goes without saying 

 that seminal plasma normally is necessary 

 for the reproductive process. To suggest that 

 artificial insemination with epididymal 

 sperm suspended in saline, successful as it is, 

 proves the dispensability of seminal plasma, 

 is to ignore the normal biologic accomplish- 

 ments of natural insemination. Neverthe- 

 less, it is a fact that artificial insemination 

 has proved highly successful in the repro- 

 duction of many types of animals. More- 

 over, the collection and analysis of the ejac- 

 ulate, coupled with artificial insemination 

 by natural or modified semen, constitute the 

 basis for much of our knowledge concerning 



