This third law is the law of stimulus, the necessity of the intervention of an external excitatory force capable of setting in motion the current of energy required for a transformation.
"The Mechanism of Life"
Stéphane Leduc
Their special function seems still somewhat obscure, and Boudier suggests that they may be excitatory organs for the dehiscence of the asci.
"Fungi: Their Nature and Uses"
Mordecai Cubitt Cooke
When the excitatory impulses are also lost, as in a total transverse lesion of the cord, the paralysed muscles are flaccid and the deep reflexes disappear.
"Manual of Surgery Volume Second: Extremities--Head--Neck. Sixth Edition."
Alexander Miles Alexis Thomson