========================================================================= Medium Yolk in Pre- Post- Sur- ---------------------------- final freezing thawing vival Diluent Extending Glycerolating[C] mix- motility motility (per- ------------ ---------------- ture[D] (percent) (percent) cent) yolk:citrate yolk:citrate (percent) ------------------------------------------------------------------------- 1 1:1 1:1 45.7 65 5 8 2 1:1 1:3 34.9 64 27 42 3 1:3 1:1 33.6 63 33 52 4 1:1 0:1 24.2 64 39 61 5 1:3 1:3 22.8 63 37 59 6 1:3 0:1 12.1 59 33 56 7 1:7 1:7 11.4 56 35 62 8 1:7 0:1 6.0 52 26 50 9 1:15 1:15 5.7 49 25 51 ------------------------------------------------------------------------- [C] This mixture included 14 percent glycerol. [D] The average initial sperm concentration was 900 x 10^{6}/ml. Sufficient extender was added to give 30 x 10^{6}/ml. at the first extension. Thus the final concentration was 15 x 10^{6} sperm/ml. after glycerolization. Since rather large changes in the percentages of yolk were used in this experiment, two further trials were conducted in which 16, 24, and 32 percent yolk in the final mixture were compared, with the final citrate percentages held constant. In these tests, 16 and 24 percent yolk maintained sperm better at all citrate levels tried than 32 percent yolk. The 16 percent level was slightly better at most of the levels of citrate tested (Fig. 3).