The author uses the word incited muscular activity for the contraction of the skeletal muscle following a percussion given by a reflex-testing hammer. This activity is called response. There are two classes of responses: the neuromuscular or reflex response and the idiomuscular response. The author analyzes the concept of the phasic reflex-responses by muscular stretch incited by the clinical percussion-method, revising the conceptions of classical authors, Wartenberg, Monrad-Krohn, etc. He thereupon exposes his own ideas. The author describes the idiomuscular response and its clinical modifications. He studies the habitual regimen of clinical co-existence between the neuromuscular response and the idiomuscular response and also the modifications of this regimen in pathological conditions. He especially refers to a phenomenon called "phenomenon of contrast of the contraction" by Barraquer-Roviralta, which appears in lesions of the posterior roots - for instance, in tabes - and consists in a loss of the reflex response with increase of the idiomuscular response.