Chemical and Physical Properties of Semen 39 



be able to define what constitutes normal fertile semen, and what 

 criteria if any, can be applied in the appraisal of ejaculated semen. 

 It may be stated at once that in spite of the wealth of information 

 gained by past and present students of semen, there is as yet no single 

 seminal characteristic known, which alone could serve as the means 

 of judging 'male fertility'. The best criterion of the fertilizing capacity 

 of spermatozoa is of course, the actual ability to fertilize the ovum. 

 This however, cannot be regarded as a laboratory test, until the 

 in vitro fertilization of the ovum has actually been accomplished 

 and the quantitative aspects of the process developed. 



In the practice of artificial insemination of cattle, male fertility 

 continues to be assessed on the basis of the 'conception rate'. At 

 the artificial insemination centres, inseminated cows which have 

 not been 'returned' by the farmers for re-insemination within three 

 months or so, are presumed to have conceived, and the proportion 

 of presumed pregnancies, expressed as the percentage of the total 

 of the first inseminations, is referred to as 'conception rate'. Nearly 

 one-third of the cow population of England is now bred by artificial 

 insemination, and among these the conception rate averages at least 

 60%. There is considerable evidence, however, that a substantial 

 proportion of cows 'returned' for re-insemination, may have also 

 conceived but that pregnancy terminated at an early stage through 

 faulty ovum implantation or embryonic death. 



Apart from the test based upon accomplished fertilization, the 

 means available at present for the evaluation of semen quality 

 include the histological and the physico-chemical methods. 



Histological examination of semen involves procedures such as 

 the determination of sperm concentration or 'density' (number of 

 spermatozoa per \fj\. or 1 ml. of semen) with a cytometer (Walton, 

 1927; Weisman, 1942); differential count of abnormal forms of 

 spermatozoa (Lagerlof, 1934; Harvey and Jackson, 1945; Lane 

 Roberts et al., 1948; Williams, 1950); bacteriological examination 

 (Gunsalus, Salisbury and Willett, 1941; Kelly, 1947; Foote and 

 Salisbury, 1948; Almquist, Prince and Reid, 1949; Wu, Elliker and 

 McKenzie, 1952-3); determination of the incidence of dead sperma- 

 tozoa by means of 'live-dead staining' methods (Lasley, Easley and 

 McKenzie, 1942; Lasley and Bogart, 1943; Madden, Herman and 

 Berousek, 1947; Crooke and Mandl, 1949; Blom, 1950; Mayer, 



