On crystal size and cooling rate.

A theoretical model is proposed which is used to derive a quantitative relationship between the critical cooling rate and average crystal size at any location within a biological specimen of given shape subject to rapid freezing. The model is applicable to the slamming, plunging or spraying methods of cryofixation provided the ice crystal size is at least 5 times greater than the size of the critical nucleus. Complete vitrification of pure water or aqueous solutions is shown to take place at cooling rates in excess of about 3 X 10(6) K/s.