404 RETINAL DISTURBANCE. 



Apparitions mer, the designation of apparitions ; to the latter, that of vis- 

 and visions. j ons ma y be given. Dreams therefore come under the latter 



class. 



The simplest form of apparition is that known among physicians as 

 Muscse voli- muscse volitantes. These are dark specks, like flies, which 

 tantes. seem to be floating in a devious course in the air. They are 

 owing to disturbances or changes in the retina. They often appear to 

 occupy the dying. 



Of visions the most common, because they can be voluntarily pro- 

 Remains of op- duced, are those which depend on the remains of impressions 

 tic impressions. j[ n the retina and optic centres. If, when we awake in the 

 morning, our eyes are turned for a moment to a window or other bright 

 object, and then closed, there still appears to the mind a spectral repre- 

 sentation of the. object, which gradually fades away. These illusions can 

 be caused to have, as it were, a movement in the dark, space before us, 

 answering to the voluntary rotation of the eyeball. Sometimes, when 

 the light is not sufficiently intense, or the nervous organs not sensitive 

 enough, the vision does not make its appearance on the closing of the 

 eyelids, but, after fastening the attention on the position in which it is ex- 

 geatofa ari- P ecte< ^ to.come, it slowly emerges at last. That it consists 

 tions and vis- in a real impression which has been made on those organs, 

 )ns ' and is not a mere product of the unaided imagination, is very 



clear from the fact that we may discern, by attentively considering it, 

 many little peculiarities which we have not had' time to notice in the 

 original object ; thus, if there has been a lace curtain, or other such well- 

 marked body before us, we can not only see in the vision the places 

 where its folds intersect the windows, but likewise, if the impression be 

 a good one, all the peculiarities of its figured pattern ; and that our 

 conclusions in these respects are correct is proved as soon as we re-open 

 our eyes. 



Between apparitions and visions is an intermediate class, of which it 

 is not my object now to say much; they may, however, be 



Deceptions. .. J . J \ . 7 . / . J 



styled deceptions. These take their origin in some outward 

 existing reality, and are exaggerations of the fancy. They are commonly 

 encountered in the evening twilight, or in places feebly illuminated. Sir 

 W. Scott says of children that lying is natural to them, and that to tell 

 the truth is an acquired habit. If they are thus by nature prone to de- 

 ceive those around them, they are none the less prone to deceive them- 

 selves. To them, a white object, faintly descried in the obscurity, is 

 easily expanded into a moving and supernatural thing. 



In a physiological sense I consider that simple apparitions arise from 

 disturbances or disease of the retina ; visions from the traces of im- 

 pressions inclosed at a former time in the corpora quadrigemina and op- 



