the interior with time sperm obtained from the reheated capsule were mixed with fresh medium centrifuged at 500 g for 10 min and then allowed to 34 swim 34 away from the centrifugate obtained from centrifugation some of the mouse and bovine sperm so obtained were shown to be capable of fertilizing a suitably mature oocyte in vitro human sperm was prepared in same way and tested in same fashion viability was assessed by morphology general motility and the appearance of active forward progressive motility no fertilizations were attempted with human spermatozoa polymer at a concentration of 3 8 dry weight liquid in culture medium containing salts lactate pyruvate but not glucose or fructose was used bovine spermatozoa encapsulated in the polymer were preferably cooled from 37 u00b0 c to 10 u00b0 c over a period of at least 6 hours a much slower rate than that found to be effective for encapsulated murine or human spermatozoa the preferred rate of temperature increase for restoring the motility of bovine spermatozoa gel to liquid transformation is also longer than for encapsulation of spermatozoa of the other two species 12 16 hours in the polymer capsules formed with rl39 117 rl39 118 and rl39 115 at present bovine spermatozoa have been maintained over an 18 hour period at least 70 of the spermatozoa displayed the typical pattern of activated progressive forward motility characteristic of viable sperm after being released from the polymer at 37 u00b0 c successful in vitro fertilization of in vitro matured bovine oocytes.