The artist has described the substance as being his own urine in a glass.
He described the substance (in 1899) as similar to titanium and (in 1900) as similar to thorium.
Loewi described the substance released by the vagus nerve as vagusstoff, which was later found to be acetylcholine.
But their officials would not describe the substance of those conversations.
Crawford took flashlight photographs of the ectoplasm, and described the substance as "plasma".
On another occasion, Murray described the substance of Boychuk's advice as "baseless".
Although no one would describe the substance of the talks, both sides described them as intense and productive.
While military officials described the substance used to disperse the crowds as tear gas, the medical commission seemed to suggest that something more toxic had been used.
They described the substance to a meeting of the Imperial Institute of France.
They did not describe the substance of that communication.