Could it be that cyanuric acid was added to milk?

I also looked 'melamine' up in Wikipedia and went to its Toxicity section.

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Qoute:

Melamine by itself is non-toxic in low doses, but when combined with cyanuric acid it can cause fatal kidney stones due to the formation of an insoluble melamine cyanurate.

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I think I had come across that 'cyanuric' thing earlier. I went back to the articles I had read. Ah, yes. It's in the report from the University of Maine Food Science and Human Nutrition Department. 

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Qoute:

He (Brian Perkin) noted that the toxicity may be related to the addition of cyanuric acid or by the addition of a melamine cyanuric acid complex, such as fire retardant.

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According to (A.A. Babayan, A.V.Aleksandryan, "Toxicological characteristics of melamine cyanurate, melamine and cyanuric acid", Zhurnal Eksperimental'noi i Klinicheskoi Meditsiny, Vol.25, 345-9 (1985). Original article in Russian.), melamine cyanurate is considered to be more toxic than either melamine or cyanuric acid alone.