I can't imagine that anyone would want an army full of squaddies shitting all over the place. Unless someone had thought up a new secret weapon under which to bury Die Fuhrer of course. So my guess (urban myth alert!) is that the suspected substance would have been thought to be bromide.

Roy H's comment about bromide being used to make better soldiers set the old grey cells working to interesting effect. The Mass Psychology of Fascism, published 1933, and written by one Wilhelm Reich (no I didn't make that one up), argued that the emotionally ecstatic displays which characterised mass identification with Nazism were linked to sexual repression on the part of the lower orders.

The theory has long since been discarded as codswallop and rightly so. But curiously enough, George Orwell uses the same idea in 1984. According to Julia, the woman he has an affair with, all the shouting and raving during the daily hate break is just repressed sex; sex which of course has been repressed by the Party precisely to engender loyalty to the party.