1. The proportion of stained spermatozoa in a ram semen-nigrosin-eosin mixture has been found to increase with the time of exposure to the stain. Five minutes is considered to be a suitable interval for practical use.2. The value obtained for the proportion of dead cells can be considerably affected by the selection of fields that are easy to count; fields should be chosen at random.3. The variation between, counts on the same smear is much larger than that expected for binomial proportions. This may be due partly to the ‘clumping’ of the dead spermatozoa and partly to the difficulties of interpretation caused by the presence of many partially stained cells.4. A significant difference was found between the estimates of the proportion dead obtained by the two experimental workers; this is thought to be due to a difference of interpretation of ‘stained’ and ‘unstained’.5. Tables are given by which to determine the approximate accuracy of counts made on a range of numbers of spermatozoa, smears and subsamples, separate tables being necessary for ram, boar and bull semen.

Testosterone was measured in the peripheral blood plasma of normal men by radioimmunoassay. The results were analysed to test for the possible existence of a circadian rhythm, for fluctuations superimposed on any such rhythm, and for day-to-day variations.

A comparison of certain features of the testis and epididymis has been made in five species of East African mammals, two of which, the rock hyrax and elephant, have abdominally situated testes.The artery to the testes was straight in the species with abdominally situated testes and there was no pampiniform plexus while in the species with scrotal testes, it was coiled in the region of the plexus. It is suggested that where the testicular artery is coiled, the testes should be regarded as basically scrotal, even if they are usually found in the abdomen post mortem.A striking increase in blood flow in the testis of the rock hyrax during sexual activity suggests that the simpler arterial pattern of the testis in testicond mammals allows a greater variation in blood flow than the more complicated arterial design associated with scrotal testes.Characteristic signs of sperm maturation occur in the epididymis of testicond mammals in contrast to the situation in artificial cryptorchidism, where normal epididymal function is completely disrupted. It is suggested that epididymal function, as well as spermatogenesis, has become modified during evolution. Evidence is given that a need for prolonged survival of spermatozoa in the mesonephric duct might have been an important primary factor in the caudal migration of gonads into a scrotum. d

A technique is described for collection of the epididymal contents from the cauda epididymidis of anaesthetized rabbits. The technique avoids undue contamination of the epididymal contents with blood or tissue fluid and overcomes the difficulty of post-mortem change. The effects of high-speed centrifugation and cold shock on the composition of epididymal plasma have also been investigated, and it has been shown that lactic dehydrogenase and glutamic\p=m-\oxaloacetic transaminase are largely intracellular constituents, whilst sodium, potassium, acid phosphatase, alkaline phosphatase and \g=b\-N-acetylglucosaminidase are extracellular. Finally, some results are presented on the overall composition of epididymal plasma in the rabbit.

Assessment of the ratio of live to dead spermatozoa showed that the ultimate loss of fertilizing capacity by the spermatozoa in both intact and gonadectomized males was not at first due to an increased incidence of dead spermatozoa in the epididymis, though progressively more dead and degenerated spermatozoa were gradually to be seen in the samples.The fertilizing capacity of the spermatozoa was lost more rapidly (within 8 days) in gonadectomized animals if they were also hypophysectomized. Administration of HCG to these animals failed to maintain normal viability in the spermatozoa.A gradual decrease in the occurrence of 'light' cells in the lining tissue of the duct is reported, following gonadectomy.It is concluded that circulating androgen is unquestionably required for the normal survival of spermatozoa in the tail of the hamster epididymis and that it probably achieves its effect through its influence on the epididymal epithelium. The findings are discussed in relation to the general hormonal control of sperm survival in the epididymis.