456 PHYSIOLOGY CHAP. 



fraction of the phenomena of mental life, our personality is no 

 monad, no indivisible entity ; the centralisation of the metameres 

 from which the brain was originally derived is while almost 

 complete from the anatomical point of view exceedingly imperfect 

 from the physiological standpoint, as is proved by the modern 

 doctrine of cerebral localisation. 



Further, the evidence of disintegration or fragmentation of 

 personality, as the double consciousness observed in hysterical sub- 

 jects, in which the primary person or supraliminal self is associated 

 or alternates with a secondary person or subliminal self, along with 

 other strange phenomena well established by psychiatry, experi- 

 mental hypnosis, and occultism, may be taken as the first indica- 

 tions, if not as direct evidence, of a possible or at least conceivable 

 segmented psychology. These phenomena are not capable of strict 

 scientific analysis, and they baffle the philosopher by their great 

 complexity, leaving him to flounder in the unexplored abysses of 

 human nature. Yet the physiologist and psychologist must not 

 spurn this study with the specious and futile argument that we 

 are not yet in a position to reconcile it with those common postu- 

 lates of physical and biological science which have been accepted 

 as intangible dogmas. Taken as a whole, these abnormal 

 phenomena (subnormal or supranormal), whether spontaneous or 

 provoked, are equivalent to vivisection experiments upon the 

 human mind. As such, they are valuable in psychological analysis, 

 because normal phenomena, owing to mental exaltation or dissocia- 

 tion, assume undue proportions, which facilitates the study of the 

 individual elements or components of the human intellect. 



We must not trespass on the field of psychiatry by entering 

 too closely into these phenomena. It is enough to draw attention 

 to one of the simplest and clearest instances of doulle conscious- 

 ness, namely that known as " automatic writing." Certain indi- 

 viduals, from congenital or acquired predisposition, strengthened 

 by practice, are able to detach part of the complex psychical 

 activities which build up their personality, and to emphasise and 

 develop the subconscious functions into a secondary self, entirely 

 separate from the primary self, which thus by automatic writing 

 reveals a psychical phenomenology which is often senseless and 

 stupid, but may be coherent, logical, and tolerably well developed. 

 These are the phenomena which Morton Prince terms "co-conscious," 

 as they coexist with the conscious phenomena of the primary 

 personality. The latter may be fully awake and engaged in con- 

 versation or otherwise, while the secondary personality expresses 

 itself mechanically in writing. 



More curious, but equally authentic, are the cases of alternating 

 personality, in which the primary self is replaced by a secondary 

 self, or the reverse, in successive and more or less extended 

 periods. Invariably in these cases of alternating personality, as 



