Take first the degree of control over the voluntary muscles. In ordinary sleep this is neither possessed nor desired; in nightmare its loss is exaggerated, in quasi-hysterical fashion, into an appalling fear; while in somnambulism,--a kind of new personality developed _ad hoc_,--the sleeper (as we shall see later on) walks on perilous ridges with steady feet. I have already said that morbid somnambulism bears to sound sleep a relation something like that which hysteria bears to normal life. But between the healthy somnambulist and the subject of nightmare we find from another point of view a contrast resembling that between the man of genius and the hysteric. The somnambulist, like the man of genius, brings into play resources which are beyond ordinary reach. On the other hand, just as in many hysterics certain ordinary powers of movement have lapsed below voluntary control, so also the dreamer who dimly wishes to move a constrained limb is often unable to send thither a sufficient current of motor energy to effect the desired change of position. That nightmare inability to move, which we thus feel in dream,--"when neither he that fleeth can flee, nor he that pursueth pursue,"--that sensation which both Homer and Virgil have selected as the type of paralysing bewilderment,[39]--this is just the _aboulia_ of the hysteric;--the condition when it takes a man half an hour to put on his hat, or when a woman sits all the morning looking at her knitting, but unable to add a stitch. "Somnambulism," however, is too vague and undefined a term for our present discussion. It will only be by a comparison with hypnotism, in the next chapter, that we can hope to get some clearer notion of "sleep-waking" states. Let us pass on to consider _entencephalic sensory faculty_,--"mind's eye" faculty,--as shown in sleep or dream. Here too we shall find the same rule to prevail as with motor faculty. That is to say, on the whole the sensory faculty is of course dimmed and inhibited by sleep; but there are nevertheless indications of a power subsisting as vividly as ever, or with even added acuteness. Baillarger in France and Griesinger in Germany (both about 1845) were among the first to call attention to the vivid images which rise before the internal vision of many persons, between sleep and waking. M. Alfred Maury, the well-known Greek scholar and antiquary, gave to these images a few years later the title of _illusions hypnagogiques_, and published a remarkable series of observations upon himself. Mr. Galton has further treated of them in his _Inquiry into Human Faculty_; and cases will be found in _Phantasms of the Living_, vol. i, pp. 390, 473, etc.