Subjective Sensations and Illusions. 817 



gest trains of thought for the dream, and they may do this without arous- 

 ing consciousness as to the sensations themselves. Thus the dreams of 

 a person may be suggested by remarks by a bystander, which the 

 dreamer will not remember. A dreamy, semi-delirious state may be ar- 

 tificially induced by the use of certain narcotics, such as the preparation 

 of cannabis indica called hachisch. Under the influence of this drug 

 the emotions are largely under the control of external impressions. 

 These are greatly distorted and exaggerated and lead to false perceptions 

 and the most extravagant ideas. These ideas are pleasurable, provided 

 the sensory impressions which originate or color them are of an agreeable 

 nature. Hence, those who indulge the use of the drug, take care befoia 

 hand that they be surrounded by agreeable things. 



CHAPTER LXXIV. 



SUBJECTIVE SENSATIONS AND ILLUSIONS. 



Subjective sensations are those which are excited in the brain by al- 

 terations not caused by external stimuli, but by some internal stimulus 

 upon the nerves of sense, or a disease or lesion of the brain. Thus, 

 persons may have for years a constant ringing sound in the ears, due 

 perhaps, to inadequate insulation of the auditory nerve from the beat- 

 ing blood vessels. Congestion of the nerves of common sensation pro- 

 duces "feelings of pain or uneasiness, a blow upon the optic nerve 

 causes a sensation of light. " In general, when nerves are stimulated 

 by abnormal causes within the body, the effects are, to produce the same 

 or similar sensations to those normally produced by the ordinary external 

 stimulus. Subjective sensations may originate in peculiar conditions of 

 the brain itself, or of the organs of sense, or of the nerve trunks. 

 They may properly be called subjective if their causes cannot be traced 

 directly to the environment, but depend on changes in the body itself. 



There are often sensations in one place which are excited by causes 

 in operation in a very different part of the body. "Disease of the hip 

 joint is often indicated by pain in the knee, irritation of the ovary will 

 cause pain under the mamma, various disorders of the liver occasion 

 pain under the left scapula;" " the sudden introduction of ice into the 

 stomach will cause intense pain in the supra-orbital region, and the same 

 pain is frequently occasioned by the presence of acid in the stomach 

 and may be very quickly relieved by its neutralization with an alkali. " 

 In many cases there is no direct nervous connection between the dis- 

 ordered locality and the place where the symptoms are felt. The con- 

 nection is indirect through a common center, and in this center it must 

 be that an afferent stimulation from a part really affected, transfers 

 itself to adjacent cells, connected with parts not affected ; the sensation 

 to them being the same as if it came from the part with which they are 



