Letter from Solly Zuckerman, on a paper 'Mitotic activity in the adult male mouse, Mus musculus L. The diurnal cycles and their relation to waking and sleeping' by W S Bullough to Gavin Rylands de Beer He has been through the paper and is 'doubtful whether it has any merit'. It is based on a paper that was previous rejected by the Journal of Endocrinology. The author hasn't paid attention to the calculated standard errors. The experiment was conduced over a twenty four hour period which is restrictive. The author 'may be on to something, but he certainly hasn't established it, and his statistical treatment appears very amateurish'. He wonder if the other paper that is being considered by the Royal Society is any better. [Published in Proceedings of the Royal Society B, 1948]. 22 November 1947