The human eye is like an immunological fortress, with its ability to exclude unwanted intruders a boon when preventing infection but a burden when trying to deliver vital medicines. | The human eye is like an immunological fortress, with its ability to exclude unwanted intruders a boon when preventing infection but a burden when trying to deliver vital medicines. Researchers in China have now turned to an unusual source—pig semen—to develop eye drops that can deliver cancer drugs to the back of the eye.