Tone and the Nilotic case system

In a number of Nilotic languages spoken in East Africa it has been shown that there exists formal marking of case based exclusively on tonal differentiation. This has been fully described in Maasai (Tucker and Mpaayei, 1955) and all investigated Kalenjin dialects (Tucker and Bryan, 1962. 1964–5). It also is clearly present in my own data on Teso, though interestingly enough it seems to be lacking in the Luo group generally.