Chang's body of work in mammalian fertilisation is large and appears in nearly 350 publications. One of his major discoveries was the effect of lowering temperature on sperm. Chang found that at a temperature of 13 °C or lower, the membrane structure and function of sperm would disintegrate, thus destroying the fertilising capacity of the sperm. This phenomenon is now commonly known as cold shock. Yet another of Chang's major discoveries was his observation on the relationship between the number of available sperm and the effective fertilisation of ova by the sperm. It was believed that the fertilisation of the egg was dependent on there being a large number of available sperm in the fertilisation process. Chang found that it was actually the physiological structure of the individual sperm that affected the actual fertilisation of the egg, and that having a large number of sperm was not necessary. He then posited that the purpose of having a large number of sperm in the fertilisation process was to allow for greater genetic recombination, in that only the strongest sperm would reach the site of fertilisation through the female reproductive tract. The process of capacitation, the maturation period of sperm that is required in order for them to be able to fertilise ova, was also amongst one of Chang's major discoveries. This observation would lead him further to find that capacitated sperm would lose capacitation if exposed to seminal plasma or blood serum, and that recapacitation could be achieved if the sperm was placed back in the uterus or the fallopian tubes.