I've read a paper on an experiment called "The Feeling of Being Stared at", which investigates a concept which on Wikipedia is called the psychic staring effect. It was first investigated by psychologist Edward B. Titchener in 1898.
The paper consistently refers to the experimental subjects as "reagents".
"In some of the experiments, the distance between the experimenter and reagent was varied for the purpose of..."
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I'm unfamiliar with this term to refer to subjects, and I assume it's because this is an old paper from 1913. My guess would be that the word means something or something that reacts, and subjects are subjected to stimuli. Is anyone familiar with this term being used generally in experiments around this time period or even today? And if so, when it fell out of fashion and replaced with what we use now: "subject".