Many disturbances and disintegrations of the personality must presently fall to be discussed. But the reader who may follow me must remember the point of view from which I am writing. The aim of my analysis is not to destroy but to fulfil;--or say, rather, my hope is that observation of the ways in which the personality tends to disintegrate may suggest methods which may tend on the other hand to its more complete integration. Such improvements upon the natural conditions of the organism are not unknown. Just as the study of hysteria deals mainly with instabilities in the threshold of consciousness, so does the study of zymotic disease deal mainly with instabilities in the constitution of the blood. The ordinary object of the physician is to check these instabilities when they occur; to restore healthy blood in the place of vitiated. The experimental biologist has a further aim. He wishes to provide men with _better_ blood than nature has bestowed; to elicit from virus and decay some element whose infusion into the veins may give immunity against microbic invasion. As the adult is safer against such attacks than the child by dint of his more advanced development, so is the immunised adult safer than the common man. The change of his blood which healthy maturity has induced has made him safe against whooping-cough. The change in his blood which we effect by injecting antitoxin makes him temporarily safe against diphtheria. We have improved upon nature;--and our artifice has been _prophylactic_ by virtue of being in a certain sense _developmental_. Even such, I trust, may be the achievement of experimental psychology in a later day. I shall be well content if in this chapter I can give hints for some future colligation of such evolutive phenomena as may lurk amid a mass of phenomena mainly dissolutive--phenomena whose records are scattered and imperfect, and have as yet only in some few directions, and by quite recent writers, been collated or systematised on any definite plan. The discussion of these disintegrations of personality needs, I think, some little clearing of the ground beforehand, if it is to avoid confusion. It will be needful to speak of concurrent and alternating streams of consciousness,--of subliminal and supraliminal strata of personality and the like;--phrases which save much trouble when used with care, but which need some words of preliminary explanation. It is not easy to realise that anything which deserves the name of consciousness can be going on within us, apart from that central stream of thought and feeling with which we identify ourselves in common life. Something of definition is needed;--not indeed of any formal or dogmatic kind;--but enough to make clear the sense given to such words as consciousness, memory, personality, in the ensuing pages.