539. I pass on to cases of the production by suggestion or self-suggestion of hyperæsthesia, - of a degree of sensory delicacy which overpasses the ordinary level, and the previous level of the subject himself.

The rudimentary state of our study of hypnotism is somewhat strangely illustrated by the fact that most of the experiments which show hyperæsthesia most delicately have been undertaken with a view of proving something else - namely, mesmeric rapport, or the mesmerisation of objects, or telepathy. In these cases the proof of rapport, telepathy, etc, generally just falls short, - because one cannot say that the action of the ordinary senses might not have reached the point necessary for the achievement, though there is often good reason to believe that the subject was supraliminally ignorant of the way in which he was, in fact, attaining the knowledge in question.

In these extreme cases, indeed, the explanation by hyperæsthesia is not always proved. There may have been telepathy, although one has not the right to assume telepathy, in view of certain slighter, but still remarkable, hyperæsthetic achievements, which are common subjects of demonstration. The ready recognition of points de repère, on the back of a card or the like, which are hardly perceptible to ordinary eyes, is one of the most usual of these performances.

In this connection the question arises as to the existence of physiological limits to the exercise of the ordinary senses. In the case of the eye a minimum visibile is generally assumed; and there is special interest in a case of clairvoyance versus cornea-reading, where, if the words were read (as appears most probable) from their reflection upon the cornea of the hypnotiser, the common view as to the minimum visibile is greatly stretched (see 539 A).

540. With regard to the other senses, whose mechanism is less capable of minute dissection, one meets problems of a rather different kind. What are the definitions of smell and touch? Touch is already split up into various factors - tactile, algesic, thermal; and thermal touch is itself a duplicate sense, depending apparently on one set of nerve-terminations adapted to perceive heat, and another set adapted to perceive cold. Taste is similarly split up; and we do not call anything taste which is not definitely referred to the mouth and adjacent regions. Smell is vaguer; and there are cognate sensations (like that of the presence of a cat) which are not referred by their subject to the nose. The study of hyperæsthesia does in this sense prepare the way for what I have termed heteræsthesia, in that it leaves us more cautious in definition as to what the senses are; it accustoms us to the notion that people become aware of things in many ways which they cannot definitely realise.

Let us now consider the evidence for heteræsthesia; - for the existence, that is to say, under hypnotic suggestion, of any form of sensibility decidedly different from those with which we are familiar. It would sound more accurate if one could say "demanding some end-organ different from those which we know that we possess." But we know too little of the range of perceptivity of these end-organs in the skin which we are gradually learning to distinguish - of the heat-feeling spots, cold-feeling spots, and the like - to be able to say for what purposes a new organ would be needed. For certain heteraesthetic sensations, indeed, as the perception of a magnetic field, one can hardly assume that any end-organ would be necessary. It is better, therefore, to speak only of modes of sensibility.

Now to any one who reflects on the evolutionary process by which, as is commonly assumed, man's organism has been developed from the simplest germ - a process which is undoubtedly still at work, and which must, so far as we can tell, continue at work for ages perhaps very far exceeding the ages already past - to any one, I say, who takes a broad view of human development, it must seem a very improbable thing that that development should at this particular moment have reached its final term; or rather, to put the question at issue in a narrower form, that this immensely complex nervous system, which has gradually become responsive in so many ways to external nature, should never again become responsive, or be recognised as responsive, in any fresh way. I can imagine no theory, except the theory that all species were created immutably as they stand to-day, which could even seem to justify the tacit assumption, still frequently met with, that new forms of human sensitivity are antecedently improbable.

They may be, and they often have been, claimed on insufficient evidence; but that they must occur some time and somehow I, for one, can hardly doubt.

Let us consider a moment in what general fashion we can conceive the differentiation of senses to have taken place.

In some sense or other we must needs attribute what I have called panoesthesia to the primal germ. We must suppose that its potential sensations were such that all actual sensations of animals and men could be got out of them. The protoplasm may itself have been capable (and in low forms may still be capable) of vague sensations of many different kinds. Or it may have been capable only of some one vague sensation, though able also to develop new forms of protoplasm with varied sensitivities.1

In either of these cases - let us take the former as somewhat the simpler to deal with - the question among sensations was one of the development of the fittest; that is to say, that, as the organism became more complex and needed sensations more definite than sufficed for the protozoon, certain sensibilities got themselves defined and stereotyped upon the organism by the evolution of end-organs. Others failed to get thus externalised; but may, for aught we know, persist nevertheless in the central organs; - say, for instance, in what for man are the optic or olfactory tracts of the brain. There will then be no apparent reason why these latent powers should not from time to time receive sufficient stimulus, either from within or from without, to make them perceptible to the waking intelligence, or perceptible at least in states (like trance) of narrow concentration.

The great variety of senses which we believe the lower animals to possess may well suggest to us that we also might have been developed thus or thus; - that we need not be surprised if the human organism should some day show a trace of any form of sensibility which the ant or the bee may have inherited along with us from the ancestral germ, although only they and not we may have thus far needed to develop it.

1 Or, as suggested by Nagel (540 A), there may have been at a certain stage mixed sense-organs, by means of which two or three sensations were perceived simultaneously.