8o TEE POPULAR SCIENCE MONTHLY 



DELUSIONS 



Bt Dk. shepherd ivory FRANZ 



GOVERNMENT HOSPITAL FOB THE INSANE 



IT is well known that sensory stimuli are not always correctly appre- 

 ciated, and that under certain conditions errors of judgment are 

 made. These errors of perception which are not infrequent with normal 

 people are called illusions and hallucinations. At times, especially in 

 the insane, we find that complex situations and less direct stimuli are 

 apprehended by an individual wrongly, and they lead to the expression 

 of beliefs which are contrary to the experience of others, or opposed to 

 generally accepted beliefs. Some of these false beliefs are called 

 delusions. As usually defined a delusion is considered to be false belief 

 not directly or immediately dependent upon definite sensory stimula- 

 tion or upon percepts, and in this respect a delusion may be differen- 

 tiated from an hallucination, a paresthesia and an illusion. 



It should be understood, however, that not all false beliefs are delu- 

 sional in nature. Some are clearly mistakes due to insufficient knowl- 

 edge. Many years ago it was commonly believed that pelicans fed their 

 young with their own blood. It was also generally held that the sun 

 revolved around the earth. These beliefs were apparently due to lack 

 of knowledge, and although the first scientist who disputed the truth 

 of either of these beliefs opposed the generally accepted belief of the 

 time, his beliefs were later held to be reasonable and not opposed to 

 experience. 



Other false beliefs may be due to memory defects. For example, if 

 on a Tuesday a man should say "To-day is Sunday," the statement 

 would be an expression of a false belief, but the expression of this belief 

 may not in itself be an indication of the presence of a delusion. If the 

 man had only recovered from the prolonged effects of a drug such as 

 alcohol or morphine, under which influence he had been since the pre- 

 ceding Saturday, or if he had just recovered consciousness after a 

 period of unconsciousness of three days, the expression of the belief that 

 the day is Sunday would not in itself indicate that he was deluded. He 

 would have good reason to believe it was Sunday. The most natural 

 and most normal belief he could have under the circumstances would 

 be that he had been drugged or unconscious and that he had just 

 awakened from a period of unconsciousness. The intervening period 

 would be for him the same as if he had been asleep. 



In a similar manner mistakes in dates may be made, which are not 

 delusional. Critics tell us that December 25, Christmas Day, is not the 

 date of the birth of the Christ, but a date established in accordance with 



