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visions; normal or induced somnambulism as hysterical somnam- 

 bulism; post-hypnotic suggestion and fixed ideas, automatic writ- 

 ing, and the dowsing-rod as the motor automatisms and fixed ideas 

 of disease. The difference between normal and abnormal disso- 

 ciated states probably depends upon differences in the lines of dis- 

 aggregation, psychical and physiological, and not upon the differ- 

 ences of process. 



If Virchow's great generalization is true, namely, that disease 

 is only life under altered conditions, we may say that the phenom 

 ena of abnormal psychology are only the normal processes of 

 the mind and brain submitted to changed conditions. One great 

 vantage-point of abnormal psychology is that by altering the con- 

 ditions at will, as we often can do, we can study the alterations in 

 the normal processes and thus find out what those processes are. 



It has been, indeed, through a study of the abnormal, that is, 

 a study of natural forces under altered conditions, that the phys- 

 ical sciences have received their development. It was by such a 

 study of abnormal phenomena that Galileo was able to demonstrate 

 the laws of inertia and of falling bodies; that v Archimedes proved 

 the theory of his lever, and that Pascal demonstrated his hydro- 

 dynamic paradox. In fact, all physical research depends upon 

 the study of abnormal phenomena. 



The Mind not a Unity 



One of the great truths taught by abnormal psychology is that 

 while the mind under ordinary conditions is for practical purposes 

 a unity, under altered conditions it may cease to be a unity, and 

 may exhibit multiple activity of a complex sort. It is even ques- 

 tionable whether under habitual conditions it is ever an absolute 

 unity, whether within certain limitations it does not always exhibit 

 a certain degree of multiplicity. It remains a problem, which I 

 have thought well worthy of special consideration at this time, to 

 investigate what those limitations are. 



Influence of the Mind on the Body 



Again, considered from the two points of view of dissociation 

 and automatism, we are able to approach those puzzling problems 

 which belong to practical medicine and which have long baffled 

 clinical research. From the earliest times to these days of scientific 

 skepticism about the veridity of phenomena which cannot be ex- 

 plained, the influence of the mind on the body for ill or for good 

 has been and is recognized. Its influence for evil is evident in the 

 nervous manifestations which mimic organic disease, in the per- 



