This hypothesis is full of difficulties. First, there is the absence of anatomical basis, of special organs and nerves. It will be necessary to return to this important point when dealing with pleasure (Chap. iii.). Nichols tells us that there is nothing to prove that nerves of pain do not exist, though they have not been experimentally established—which is indeed something; that histological research could not determine in the peripheral apparatus what belongs to touch and what belongs to pain; and that proof must be deduced from cases of tactile sensation without pain and _vice versâ_—which fails to constitute any degree of proof. Moreover, the distinction set up between displeasure (moral pain?) and physical pain is arbitrary, factitious, wholly unjustified. There is, however, a still less admissible distinction. Strong expressly declares that he limits himself to pains localised on the cutaneous surface. Now by what right can we cut off the group of physical—strictly physical—pains, the states of torture originating in the internal organs, the multiple neuralgias as intolerable as any external pain, without speaking of discomfort, prostration, exhaustion? Are these also sensations, or something else? We are not told. Finally—and Strong himself has stated the objection—it must be acknowledged that we should here have a strange kind of sensations which do not externalise themselves. While other impressions, visual, auditory, tactile, gustatory, olfactive, are referred to causes which provoke them, the pains of a prick, a cut, a burn remain strictly subjective and are not located in the needle, the knife, the burning coal, as we locate a sound in the bell, a bitter taste in absinth. The only possible reply (which the partisans of pain-sensation have not made) would be that this phenomenon has a character of its own; it always remains a sensation, and never becomes a perception, whence the absence of externalisation. But then why assimilate it to blue or red? Moreover, pain-sensation, as it exists in the adult, approaches so closely to the affective state, that what is essential in the doctrine of pain-sensation vanishes. Whatever may be thought of the probability of some future discovery of terminal organs for physical pain, as Rutgers Marshall remarks, it must be agreed that there is no proof of the existence in the environment of a special stimulus to which physical pain specially corresponds, and for that reason also it would be a great mistake to place in the well-determined class “sensation,” a mental state which lacks one of the most marked characteristics of sensation in general. That conclusion is mine also. The opposite doctrine, which has of late been called the _quale_-theory, is often maintained in an unsatisfactory form, because in fact it reduces itself to an affirmation of _quantity_. The pain which accompanies sensation may depend either on its intensity or on its quality alone.