What are the requirements for a valid donatio mortis causa?

The requirements of a valid donatio mortis causa were set forth by Lord Russell C.J. in the classic case of Cain v. Moon [1896] 2 Q.B. 283 (D.C.), where he said at p. 286: "It is further conceded for an effectual donatio mortis causa three things must combine: first, the gift or donation must have been made in contemplation, though not necessarily in expectation, of death; secondly, there must have been delivery to the donee of the subject-matter of the gift; and, thirdly, the gift must be made under such circumstances as shew that the thing is to revert to the donor in case he should recover. This last requirement is sometimes put somewhat differently, and it is said that the gift must be made under circumstances shewing that it is to take effect only if the death of the donor follows; it is not necessary to say which way of putting it is the better."