558 SOMNAMBULISM. 



optic thalami are brought out sometimes with more and sometimes with 

 less force, there is every grade of intensity presented, from those floating 

 indistinct aerial scenes, which seem scarcely to leave the slightest trace 

 behind them, to those which, in spite of their outraging all reality, and 

 even all probability, leave us in a horror-stricken state ; such as, for ex- 

 ample, the celebrated dream of the Emperor Caligula, in which he thought 

 that the sea spoke to him. Yet there can be no doubt that in all these 

 cases, no matter how indistinct or energetic, how false or how true, hoAV 



d* i n un narmon ^ ous as a whole, or how contradictory and grotesque, 

 der which the elements of which all dreams are composed are impres- 

 dreams arise. g ' ons Q ^ings t h at we have seen or heard, or which have 

 been otherwise submitted to the senses, the traces of which still remain 

 imprinted in the registering ganglia of the brain. During the day, while 

 we are exposed to light, and sounds, and other sources of disturbance, the 

 impressions arising therefrom totally overpower, by reason of their new- 

 ness and intensity, these ancient residues, so that the attention of the 

 mind, in a state of health, is never directed to them ; but when we close 

 our eyes in the silence of night, all such external impressions are at an 

 end, the organs of sense, sight, hearing, smell, and touch, are successive- 

 ly benumbed, and there is nothing to prevent the mind thus separated 

 from outer things from occupying itself with these old impressions, any 

 one or more of which, through accidental circumstances, presents itself 

 in vigor, and a dream is the result. 



The phenomena of dreams therefore illustrate, in a significant manner, 

 the remarks that we have made respecting the functions of the cephalic 

 ganglia of insects as magazines for the registry of impressions received 

 by the organs of sense. No explanation of dreaming can be possibly 

 given without admitting for a part of the human brain a like duty. The 

 important advantages which accrue to our physiological explanations of 

 the action of the human mind from the admission of this doctrine have 

 already been dwelt upon. 



Connected with dreams, and being, indeed, a dream carried into action, 

 Somnambu- i g somnambulism, or sleep-walking, of which there are several 

 iism. grades, from mere sleep-conversation and sleep-crying to the 



actual performance of difficult and even hazardous feats. The young in- 

 fant evinces its discomforts by crying in its slumber, yet it can be com- 

 forted without awaking by the well-known voice of its mother. Chil- 

 dren often show a propensity to talking in their sleep, and can sometimes 

 be brought to give a few rational replies to inquiries put to them. At 

 their time of life, the disposition is more frequently manifested to get out 

 of bed and move about the house, or even out into the open air under the 

 influence of a dream. When sleep-walking occurs in the adult, it is lia- 

 ble to be accompanied by actions of an apparently connected kind, though 



