Of recent years, however, our knowledge of hallucinations has been largely augmented from two distinct sources. On the one hand, a systematic attempt has been made to study the spontaneous non-recurrent hallucinations occurring amongst normal persons; on the other hand, wider knowledge of hypnotism and the discovery of various processes for inducing hallucinations has afforded facilities for the experimental investigation of their nature, mechanism, and genesis, both in the trance and in waking life. The hallucinations, indeed, of the ordinary hypnotic subject, with which the public has been familiarised by platform demonstrations, are possibly not sensory at all. When a hypnotised lad eats tallow-candle for sponge-cake, drinks ink for champagne, or professes to see a lighted candle at the end of the operator's finger, we may conclude, if the performance is a genuine one, that a false belief has been engendered in his mind; but we have, in most cases, no evidence that this belief includes any sensory element. In many laboratory experiments, however, there can be little question that a complete sensory hallucination is induced, and that what the subject professes to see and hear is as real to him as the furniture or the person of the operator. One or two such cases have been quoted in a previous chapter (Chap. III., p. 68). The nature and reaction of these hypnotic hallucinations have been investigated with much ingenuity by various Continental observers.[93] MM. Binet and Féré, to quote the best-known series of experiments, have found, speaking generally, that the hallucinatory percept behaves under various conditions precisely as if it were a real percept. Thus, if the subject is told to see a picture on a blank card, he will not only see the picture at the time, but he will be able subsequently to pick out the card, recognising it by means of the hallucinatory picture impressed on it, from a number of similar cards. If the card is inverted, he will see the picture upside-down; if a magnifying glass is interposed, he will see the picture enlarged; viewed through a prism, it will appear doubled; it will be reflected in a mirror; and if the hallucinatory image consists of written or printed words, he will see the writing in the mirror inverted. Hallucinatory colours will develop after-images of the complementary colour, precisely as if coloured surfaces were actually present to the eyes of the _halluciné;_ and a mixture of these hallucinatory colours will produce the appropriate third colour. If other proof were needed of the sensory nature of the induced affection, MM. Binet and Féré find it in the observation that with cataleptic subjects who have lost the sensitiveness of the cornea and conjunctiva, this sensitiveness is restored when a visual hallucination is enjoined upon them. M. Pierre Janet, in _L'Automatisme Psychologique_, has recorded a similar restoration of sensitiveness in