Fear is more manifest in birds than in any other animal. We sometimes see jugglers, as a proof of their magic power, take a little bird in their hand and lay it on its back, showing that it no longer moves, although it might easily fly away. This is an old experiment which was studied by the celebrated Jesuit Athanasius Kirchner, professor in the Roman College, who published a book in 1646 with the strange title of '_Ars magna lucis et umbræ_.’ In the chapter '_De imaginatione gallinæ_,’ he describes the following experiment: If the feet of a hen are tied together, and she is then laid upon the floor, she will at first try to free herself by moving her body and flapping her wings, but when she perceives that all attempts are vain, she remains quiet. If, as soon as she is motionless, a line is drawn on the floor with a piece of chalk, beginning near her eye, the bird will not try to escape even after the feet are loosed, nor even when she is coaxed to move. Many of us, when boys, have captured a hen, screamed into her ear, and then, having put her head under her wing, have laid her breast upwards on the table, saying that she was asleep. This trick, known I believe in many countries, may be considered as another form of the _experimentum mirabile_ of Kirchner. No physiologist had occupied himself with this phenomenon until Czermak, in a treatise presented to the Academy of Sciences of Vienna in 1872, maintained that it arose from an hypnotic state, or momentary somnolence. But this hypothesis does not explain why the breathing is laboured, the eyes staring, why the animals are unable to move even when touched, nor why their comb and wittles are so pale, which is not the case in sleep. Preyer was the first to declare that these effects are due to fright, and as there was no word in the German language expressing the condition of a man overcome with fright, who is incapable of speaking, moving, or thinking, he called it _cataplexy_.[31] From his work bearing this title I extract a few observations.