Experiments conducted by M. Pawlow and his pupils add confirmation to the view that “all physiological phenomena may be completely studied as if psychical phenomena had no existence.”〔Zeliony (1906b: 81) paraphrases a sentence of Leibniz — "Le corps se développe méchaniquement et les lois méchaniques ne sont jamais violées dans les mouvements naturels; tout se fait dans les âmes comme s'il n'y avait pas de corps, et tout se fait dans le corps comme s'il n'y avait pas d'âme." — as "On peut étudier tous les phénomènes physiologiques comme si les phénomènes psychiques n'existaient pas."〕 Direct excitation of the mouth cavity of a dog produces an “unconditional” reflex secretion of the saliva. In case the exciting substance is something the dog eats, the secretion is thick; if it be one that the dog refuses, the secretion is more liquid. Any other excitant, acting on any sense whatever (or any combination of excitants), may provoke a “conditional” reflex secretion of either kind, provided it has previously acted on the animal conjointly with another excitant which has produced an unconditional reflex. The conditional reflexes are very instable and variable. But the exact conditions of their origin, their force and their disappearance can be stated in physiological terms. The so-called psychical excitants are identical with these conditional reflexes (Delabarre 1910: 85–86).

A conditioned alimentary reflex was established to the simultaneous application of the tone of a pneumatic tuning-fork, which was considerably damped by being placed within a wooden box coated with wool, and of a visual stimulus of three electric lamps placed in front of the dog in the slightly shaded room (Pavlov 1927: 142–143 (VIII )).

An alimentary reflex was established in a dog to a compound stimulus made up of the sound of a whistle and the sound of the tone d sharp of a pneumatic tuning-fork. Both these sounds appeared to the human ear to be of equal intensity, and both when tested separately elicited a secretion of 19 drops of saliva during one minute. In addition to this, another compound stimulus was established, made up of the same sound of the whistle plus the tone a of a tuning-fork of weaker intensity. When tested separately the whistle in this case elicited a secretion of seven drops of saliva during thirty seconds, and the tone only one drop (Pavlov 1927: 143 (VIII )).