COINAGES OF THE BRAIN. 309 



to constitute vision, as pictures are constantly painted upon the retina 

 which are never discerned. Now it is possible for this perceptive 

 part of the brain to be thrown into an active condition quite inde- 

 pendent of the normal stimulus conducted to it from the retina, and 

 under these circumstances the person apparently sees an object 

 which, by the law of our nature, is projected by him a certain distance 

 before the eye. This is common enough in fevers and in delirium 

 tremens, where patients see people and animals around them whose 

 reality is such that the memory of these becomes a part of the 

 experience of their future lives. In mental derangements these 

 hallucinations are also common, and patients see objects and hear 

 voices which have no external existence. So it is in our dreams, 

 from which we may be suddenly aroused by a great noise where all 

 is still around, the auditory perceptive centre of the brain having been 

 abnormally excited. 



" In normal conditions the sight of an object implies the painting 

 of it on the retina, as the hearing a noise implies the vibration of 

 the drum of the ear. If sight and hearing occur without these 

 normal excitants of the nerves, the brain must have been stimulated 

 from within, and the impressions are abnormal and subjective. 



"At the present time we have no knowledge that anything in the 

 likeness of a ghost or anything that has not a material basis can 

 excite an image on the retina ; whereas we do know that under 

 abnormal conditions the brain may be stimulated so as to produce a 

 visual impression independent of any such image on the retina. The 

 probabilities are then immensely in favour of the appearance which 

 the Doctor saw being subjective rather than objective. We have 

 only to suppose that those very common abnormal conditions of 

 brain which are observed in bad health may occur under exceptional 

 circumstances in an otherwise healthy organ to account for the occa- 

 sional appearance of ghosts. 



"The probabilities are also in favour of this view from other con- 

 siderations. First, there seems no reason why the spirits of another 

 world should prefer midnight for their visits, but the reasons are 

 obvious why we should conjure them up at that time. Then, again, 

 the want of individuality shown by this particular ghost : an ordinary 

 mortal would find it very difficult to put himself 'in exactly the same 

 place and attitude as before ' on his appearance a second time, as 

 this apparition did, and then so dependent was it upon the observer, 

 that when the latter put his arm up it was gone, and the same oc- 

 curred on the second occasion on another movement. How these 

 movements of the Doctor could have affected a real object does not 

 seem clear, nor why it could not be gazed at from different points 

 of view. It may be noticed, too, that its nearness -corresponded 

 with the focussing of the Doctor's eyes to objects close around him." 



