You need a cold scientific heart to appreciate this documentary of Pavlov's research into the 'conditioned reflex'. A series of agonising animal experiments is elucidated, this being a silent, by an onslaught of inter-titles, five consecutively at one point. Sights include dogs with their faces cut, so their saliva drips externally and measurably, dogs with bits of their brain removed, just to see what happens, chimps given electric shocks to confirm data that might be readily surmised. Pudovkin's chore (his first feature assignment) was to find a mise-en-scène to record these dismal tableaux - in theory an interesting challenge. In practice, except for lab-coat audiences, any screening is likely to be punctuated by the soft thud of the exit door.