# Popular Science Monthly/Volume 86/January 1915/Delusions

Layout 4
* DELUSIONS
By Dr. SHEPHERD IVORY FRANZ
GOVERNMENT HOSPITAL FOR THE INSANE
IT is well known that sensory stimuli are not always correctly appreciated, 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 stimulation or upon percepts, and in this respect a delusion may be differentiated from an hallucination, a paresthesia and an illusion.
It should be understood, however, that not all false beliefs are delusional in nature. Some are clearly mistakes due to insufficient knowledge. 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 preceding 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 ​the relics of pagan observances. Such a belief in the date of the nativity of the Christ is quite consistent with the beliefs of one’s neighbors and with one’s education and experiences.
Beliefs which are widespread and which may be called social beliefs, even though they be false, are not technically considered to be delusions. There are many popular beliefs of this kind which have no foundation in fact. The childish beliefs that it is unlucky to walk under a ladder, or to permit a pin to remain on the street if you see it, or to walk upon the cracks in the sidewalk, are examples of these. Such beliefs have probably arisen in more primitive conditions of life and the beliefs have been handed down from generation to generation, although not always in the same specific way. It has been suggested that the widespread belief regarding the harm which may ensue from leaving a pin on a pathway is due to a tradition which has come from the time when shoes and other protective devices for the feet were not as commonly used as they are at the present time. It may also have been due to the fact that these implements were expensive at one time, and that it was an indication of extravagance or lack of care if such objects were not picked up. Similarly, the belief in ghosts is also widespread and is probably the remnant of the mysterious ideas which were prevalent among primitive peoples as explanations of those things which could not be understood or explained in simple terms.
The mental association in the relation of cause and effect of two occurrences because two events have at one time been encountered in a temporal series is frequently met with among the uneducated. Similar causal connectives are believed in by those who, although educated, have not sufficient knowledge of the conditions of the phenomena with which they deal. The belief that certain individuals had supernatural powers or were in league with the devil was widespread among all classes several hundred years ago, and many people were whipped or burned because they were thought to be witches and capable of exerting an evil influence on others, such as producing sickness and death. The occurrence of sudden illness following certain actions of visitors was responsible for some of these beliefs, although the causative connection was not apparent. In these cases a certain mental “set” or attitude (the general belief in the supernatural) was the determining element which resulted in the individual beliefs. At the present time such beliefs are found among the uneducated, and they are especially numerous in communities which are isolated to a great extent from the rest of the world. Thus, the screeching of an owl is believed by some to portend coming misfortune; a dog howling at night means that some one had died or is going to die; the appearance of a strange black cat in one’s house is a sign of approaching illness or ill luck (although in certain communities it is considered lucky); crows foretell misfortune; etc.
​The belief that in some yet unexplored region of the earth or on some of the other planets, e.g., Mars, there is to be found a race of beings intellectually, morally and physically superior to the remainder of mankind is a belief of a different character from those already considered. In regard to this kind of belief we have no definite evidence that gives us the right to say that this is not true, but neither has the individual any evidence that the belief corresponds with actual fact. Such a belief may arise because of some religious considerations, as, for example, that since the known races of man are imperfect God has also created perfect men, or has caused a race of superior beings to be developed. Or such a belief may be the consequence of a vivid dream, or a too realistic acceptance of a novelist’s tale. Such a belief corresponds with the character of the belief of a child in the phenomena of birth, that babies are brought by storks or are to be found in cabbage patches, or with the belief that the moon is made of green cheese, or that there is a race of giants which eat ordinary-sized men, or that there are good and bad fairies which oversee the actions of man and reward or punish accordingly.
All of the beliefs which we have considered may be false, but simply because of their falsity they are not necessarily delusions. Characteristics other than that of falsity must be present to warrant the designation of a particular belief a delusion. Let us consider the false belief regarding the day of the week. If the individual who expresses the belief that “to-day is Sunday” when in reality it be Tuesday does not listen to reason, if, for example, he is taken to various churches and is shown that these buildings are closed at the time of day that Sunday services are announced upon the bulletin boards, and if he is taken to the business districts and is shown that the shops are open and that people are coming and going and making purchases as on a week day, and if, furthermore, the newsboys with morning or evening papers sell him a copy which shows by its date line that it is issued on Tuesday, and he still persists in his belief, there is something added to the false belief. If these evidences do not sufficiently appeal to his reason so that he gives up the belief, it may be said that, in addition to being false, the belief is unreasonable and opposed to the experiences of others in his community. There is, therefore, more reason for calling the false belief a delusion.
Although mistakes (such as that of the day of the week) may result in appropriate kinds of reactions, this has been considered to be a typical characteristic of delusions. Certain false beliefs are, however, of such a character that they lead to no reaction, although most frequently delusions do bring about behavior appropriate to the belief. The association of special activities with special beliefs is not any more characteristic of delusions than of true beliefs, and the fact that a false belief is ​accompanied by behavior appropriate to the belief does not warrant the conclusion that the false belief is a delusion. The firm belief of the negro in voodoo, or of the ignorant peasant in fairies, banshees and ghosts, may result in particular types of reactions. The beliefs may be associated with behavior appropriate to the beliefs and even give rise to actions which are similar to the reactions of the insane. It must be recognized, however, that these beliefs are often consistent with the individual’s previous experience and with his education. If such beliefs were held by an educated man, they would be inconsistent with his previous life and his environment; and since they are opposed to the experience and beliefs of his friends and acquaintances and bring about particular reactions on his part, we would consider them to be delusions. The ignorant negro who lies on his back when he has a pain in the abdomen or in some other part of his body, and loudly calls for his spirit to return to him shows by his actions that he believes the pain is an indication that his spirit is departing from him. His belief, however, is quite consistent with those of his neighbors, the remainder of his tribe, and they are very effective causes of action.
Under certain conditions individuals may have false beliefs, and these false beliefs for them be scientifically not delusions, although similar beliefs on the part of others would be considered delusional. Thus, for example, a child may believe that the moon is made of green cheese. This may be firmly fixed. It is not, of course, dependent upon immediate sensory stimulation and can not be corrected by an appeal to reason, but this belief is perfectly consistent with the child’s previous education and training, and it does not bring about any particular mode of reaction. In the same way the belief that the sun revolves round the earth may be held by many and may, on the other hand, be quite consistent with the experience and belief of the individual’s fellows, and possibly may not be corrected by an appeal to reason.
Nor is it necessary always that the delusion be a false belief. It is sometimes only necessary that the reasoning by which the individual arrives at the conclusion be abnormal or false. Thus, the belief that at the North Pole or at the top of a mountain a particular kind of rock may be found may be quite true if it is tested by experience. Lacking such experience and assuming or concluding that the special kind of rock is to be found because one has heard God whispering to him gives the false belief a character quite different from the other false beliefs which have been considered. Such a belief is rightly called a delusion, even though the truth of the fact be demonstrable. The delusional element in such a case is not necessarily the falsity of the belief, but the manner in which the conclusion or belief was attained.
Delusions have many characters. Some of them are held for only a brief period of time; they give place to other beliefs which are equally ​fleeting, and for this reason they are called changeable. On the other hand, certain of these delusions are fixed. They persist for long periods of time, and although they may not remain rigidly the same, their general character persists in spite of slight alterations or elaborations.
One may also consider the delusions from another standpoint. Some of them have very few mental connections, and they do not result in forms of activity which are combined with the remainder of the individual’s mentality. Apparently they do not become an integral part of his personality and they do not appear to affect him in many ways. His life is carried on as though these beliefs were not present. Such delusions we call unsystematized. Opposed to them we have others in which there is greater or less systematization. The belief of the patient with general paralysis of the insane that he is wealthy causes him to go out and order dozens of horses, to purchase hundreds of knives or razors, to dine at the most expensive restaurants, to commit all kinds of absurd actions which are quite consistent with his beliefs, but which are inconsistent with the experience of his neighbors. Such delusions which lead to appropriate reactions, and which dominate the activities and mind of the individual are spoken of as systematized. They have become a part of the individual.
From another standpoint delusions have been divided into a number of classes in accordance with the ways in which the ideas have relation to the individual. We may speak, therefore, of somatopsychic delusions when the delusions refer to the body, of autopsychic delusions when they refer to the personality, and of allopsychic delusions when they refer to the external world. These different classes are not always distinct, and it is not always possible to classify all delusions in this manner. As examples of these delusions the following may be cited: of the somatopsychic, the individual may believe there is a snake or rabbit in the abdomen, or that the abdomen does not contain its full quota of organs, or that the individual has lost a leg or that the whole body is missing; of the autopsychic, delusions of poisoning (possibly also somatopsychic), the individual has very great strength or power, he has a hypnotic eye; of the allopsychic, those in relation to the external world, the individual may be a Messiah, he has committed the unpardonable sin. There are many varieties of these referring to the different parts of the body and to the different relations of parts, and at the same time the somatopsychic, the allopsychic and the autopsychic may be compounded into one.
Some delusions have a gradual growth, others are almost fully developed in an instant. The latter are usually found associated with hallucinations, or strictly speaking, they themselves may be hallucinations. If we consider the mode of development of one of these delusions, we shall realize this. Let us say, for example, that an individual ​expresses a belief that he is a king. This delusion, when analyzed, or carefully observed during its development, is found to result from processes like the following. The individual has always been poor; he has had very great difficulty in making sufficient money to purchase for himself food of the character he craves, or to buy clothes to keep himself clean and respectable in appearance. At times, because his views of life have been different from those of his companions, he has found that he has been associated with other people of his own financial situation with whom he has not been en rapport. Their mental and moral coarseness has jarred upon him and caused him to believe that he is somehow and in certain particulars quite different from those with whom he normally associates. Then he finds it difficult to obtain a position. Owing to his inefficiency he loses one position after another, and because of his belief that he is different from his co-workers, there comes the next step in the delusion formation, the belief that people are down upon him, or are persecuting him. The final step is easy. The reasons for the persecution are sought; he considers various possibilities; he thinks about his past life, of the various positions from which he has been separated owing to no fault of his own (as he thinks); he sees no definite connection between the losses of his positions and his own incompetency, or between his lack of harmony with his fellow workmen and his own mental condition; he begins to believe that there must be some united effort to bring about these adverse conditions. Sometimes he believes this external influence is exerted by the Masons; sometimes it is one or other of the churches; and at other times he believes his difficulty has been due to the fact that his social position, if known, would be higher than that of those who persecute him. Eventually he comes to believe that he is a legitimate son of a certain ruler, and that all of his troubles have been due to the fact that in childhood, or perhaps in babyhood, another infant or child was substituted for him and that various difficulties have been made to prevent his assuming his proper place and to keep him down. From these beliefs it is an easy step to the belief that he is to be the lawful king when his supposed father dies. In general, such is the mode of development of the so-called systematized delusion which arises gradually, and which is thought out.
On the other hand, delusions may arise suddenly as if by inspiration. These latter, as has been previously suggested, usually come because of particular kinds of hallucinations which convey messages indicating the individual’s supposed greatness or his unworthiness. Here the auditory hallucinations usually play the most important part. The voice of God may be heard telling him that he is the Messiah, or he hears voices constantly saying that he must be kept out of the way in order that another may have the place which lawfully belongs to him, ​or he hears a voice calling him evil names, and in the presence of such hallucinations, a delusion may suddenly arise. Other delusions of apparently sudden origin probably arise from other causes, some of them being the end result of a number of experiences, hallucinatory it may be, no one of which by itself has been sufficiently powerful to beget a delusion.
The somatopsychic delusions, Southard has well shown, may arise because of, or be concomitant with, stimuli resulting in particular kinds of sensation in particular parts of the body. Thus, he describes the case of a woman who expressed the belief that she had been shot in the breast with a “seven-shooter.” The patient could not show any signs of a wound, nor were there any external signs visible. There were noted pleuritic friction sounds and the autopsy revealed a fibrous pleurisy at the point at which she believed she had been shot. Whether or not the form of the delusion, namely, the belief in being shot, was due to other experiences, can not be determined. In this case the conclusion that there is a relation of the particular pathological condition of the pleura and the definite ideational localization of the point of the shot with the somatopsychic delusion is not only suggested, but almost forced upon us. The ideational selection of the particular weapon (a seven-shooter) may be indicative of other causes which acted in conjunction with the abnormal sensations.
Other cases which Southard has reported have equally suggestive histories indicating that the abnormal sensations from different parts of the body may give rise to delusions of a somatopsychic character. Thus, he has recorded the case of a man who complained of torpidity of the bowels. This patient almost constantly kneaded his right chest and abdomen because of this supposed condition. At the autopsy a number of pathological states were found in the region to which he referred his delusion, and one of these, namely, the right lung was adherent to the pleura, is sufficient to mention. Another patient complained that his stomach was always full and that he could not eat, and this belief was found to be associated with the pathological finding of intestinal obstruction from cancer. In this case probably the passage of food stuffs from the stomach into and through the intestines was retarded, and it is not difficult to conclude that the belief that the stomach was full had, partially at least, its origin in, or was built upon the foundation of, the abnormal sensations which accompanied the morbid modes of gastric and intestinal activity. The accumulation of cerumen in the ear of another patient was accompanied by the belief that bugs or buzzing flies were present.
Two other cases in which no peripheral lesions were found to correspond with the delusions are cases in which cerebral lesions were found to accompany the beliefs, (1) that the insides were gone and, ​(2) that there was gravel in the head. The examination of the brain of the first of these cases revealed lesions in the optic thalamus. When we recall the fact that the thalamus is a subsidiary, although very important, sensory ganglion which receives the nervous impulses corresponding with the sensations of touch, pressure, temperature and pain, before these impulses are passed onwards to the cerebral cortex, and that in the non-insane lesions of this ganglionic mass result in anæsthesias, it is not difficult to understand that this particular cerebral lesion may have a very definite relation to the belief that the insides are gone. A similar correlation has also been recorded by Southard in the case in which the belief that “the insides were gone” was associated with a lesion in the cerebral postcentral gyri (sensory center).
It will be noted that these cases in which somatopsychic delusions are associated with variations in the sensations from the bodily periphery resemble those conditions which are grouped under the general heading of illusions. In certain cases those beliefs which are apparently delusions might very readily be considered to be paresthesias (illusions), but there is one particular in which they sometimes differ, viz., the delusions can not be correlated with definite changes in parts of the body until after death. This is especially true for those cases in which the delusion or false belief has been associated with a lesion of part of the cerebrum. If we should carefully and consistently omit from the class of delusions all those conditions in which there are concomitant physical abnormalities which might result in sensory abnormalities, we should probably classify the above cases of Southard with illusions or hallucinations. Since, however, many of the physical pathological conditions can not be determined until after death, we should need to withhold any particular designation until after that event, and an accurate designation could not then be made unless an autopsy were performed. It would therefore not be possible to distinguish between delusions and illusions and hallucinations. Obviously the matter must be settled in a more practical manner and it appears best to designate the more definite interpretative elaborations as delusions regardless of their source. Thus, internal ear diseases may result in sensations which give rise to the reports that “there is a buzzing in my ears,” or “people are talking about me,” or “there are bees in my head.” Since it is not possible to determine in every case the definite relation of an idea to a particular stimulation the interpretative additions of the last two forms of reaction give warrant for the designation of delusion. The indefiniteness of the “buzzing in my ears” is similar to the well-known paresthesias of tingling and formication, and may be classed with these, even though the morbid process leading to the abnormal sensations be unknown. The interpretative elaboration may in these cases be the only criterion differentiating the delusion from an hallucination or an illusion. ​On the other hand, there are numerous delusions which are undoubtedly due to what Freud and his school call a “wish fulfilment.” Burrow had described such a case. An unmarried woman for a number of years had complained of weakness, indigestion, distension of the abdomen, pain in the back and groin, which conditions, as far as could be determined, were not associated with any abnormal physical state. A psychoanalysis of this patient showed that she had had very great desires to be married; her dreams were of marriage and of bearing children; and her mental life had been colored by or made up largely of these wishes. The physical conditions of which she complained were taken by Burrow to be the outward signs of the conditions which she hoped she might have, namely, those of pregnancy as a result of marriage. Jones has also well described a case of a similar nature. This woman exhibited erythrophobia, i.e., fear of red, and at the same time she believed that she was responsible for or had actually caused the death of her mother. A careful mental examination showed that for many years she had been compelled to remain at home to take care of her mother, who was an invalid, that because of this she had been unable to have pleasures similar to those which she found girls of her age were having, and from time to time these conditions led to rebellious ideas. The health of her mother improved to such an extent that she was enabled to go to college or school and thus again take up her life in association with other girls. At school there was a debate in which she took part and in which, as one of the contestants on one side, she wore a red shield on her arm. Subsequent to this event she dreamed of seeing her mother lying dead, in a room on the wall of which there was a red shield. On account of worry over her dream, she went home, taking the red shield with her. She was pleased to find her mother very well and, laughingly explaining her fears, she pinned the red shield on the wall of her mother’s room. A day or two later upon awakening in the morning, she went to see her mother and found her dead in bed. Thence, it is explained, originated her belief that the act of pinning the red badge upon her mother’s wall had something to do with the death of her mother, and thence also arose the fear of red. It was also learned that because of the lack of pleasure in life she had at times considered how much better off she would be if her mother were dead, and perhaps had also unconsciously wished for such a solution of her difficulties. When, however, there was accomplished the actual result which she had wished, her action in placing the red shield upon her mother’s wall became prominent in her mind and she believed she had been warned about this in her dream.
Numerous other cases of a similar character might be cited. Most if not all, delusions are interpreted by the Freudian school in this manner. Brill, for example, interprets certain delusions of grandeur ​as being due to an overestimation of the self (of a sexual character), and the Freudian conception of paranoia, with its fixed and systematized delusions, is that it is a defense reaction of this nature. The symptoms are due to unconscious elements which act in a fashion somewhat similar to, although more powerful than, conscious ideas. These types or cases may be considered to be somewhat different from those of Southard in that they are of an ideational rather than of a sensory type.
On the other hand, we sometimes find delusions which can not be considered strictly ideational or strictly sensory in character, and it is very likely that many of the so-called ideational cases have certain sensory elements, and on the other hand that certain of the sensory cases have ideational elements in them. Such a case, with details learned at a time when the delusion was at its height, is the following; the patient was a woman who had been in love with a young man whom her mother considered to be entirely unsuitable, and because of this kept the man away from the house and, by her insistence, practically compelled the daughter to marry another man who was wealthy and socially more eligible. The man whom she married she did not love and, in fact, very much disliked. She bore several children to him, but believed that their relations were not morally right. Because of her ideas and her dislike for her husband she had lacked normal enjoyment in her married life and had frequently longed for death. Eventually she exhibited signs of insanity and was committed to a hospital. She continually said she was dead, that the physician might cut off her finger or her arm or her head without finding a drop of blood. She was not particularly untidy; she could do accustomed things very well; she dressed herself; she walked and talked and in her actions gave a lie to the beliefs which she expressed, but it was impossible to shake her belief either by reference to her acts or in any other manner. She was completely anesthetic and analgesic. This case shows physical signs, namely, anesthesia and analgesia, which may be correlated or believed to be correlated with the delusion, and on the other hand there are elements in the history similar to those which were found in the cases of Burrow and Jones. It was not determinable whether the anesthesia preceded the belief in her non-existence or the reverse.
A fourth class of delusions is not infrequently encountered. In cases of arteriosclerotic or senile dementias or in a Korsakow’s syndrome patients frequently recount their journeys of the night before; they tell how they had been fishing the previous day; they had been brought to this hotel (the hospital) an hour or two ago, or have had visits from friends, when none of these things had occurred. Here the delusion appears to be based upon memory lapses or defects. The patient does not remember the occurrences of yesterday, even those of the same ​morning, and the memory gaps are filled out by the patient, often with those occurrences which the patient would like to have had occurred. In this way such delusions may be considered to be allied to the ideational type, those of wish fulfilment which were described above.
An amnesia may lead to a delusion or false belief regarding the locality of a given place. An excellent example of this has been described by Alzheimer. A Russian who had emigrated, and located in Frankfurt, was taken to a hospital, where he insisted that he was in Russia. He could not recall any of the incidents of his removal from Russia and the period of time between his emigration from Russia until his admission to the hospital was lost from memory. The most natural conclusion for the patient under these circumstances was that he continued to be in Russia. Such a disorientation may be considered to be a delusion due to the lack of recognition of dissimilarities.
Kraepelin cites a somewhat similar case, due, however, to a different kind of memory defect, which was described by Ganser. This patient was a boy who had been admitted to the Munich psychiatric hospital who insisted that he was in Vienna. He also believed that he had been asked to join a company for the development of the Sahara Desert, that he had been in London to consult with others regarding this, and had just returned to Vienna in a balloon. The whole story was bizarre and apparently without reason, until it was subsequently learned that the patient had borrowed practically the whole system of ideas from a novel which he had read some time previously. He had forgotten the fact that he had read the book, but he remembered the incidents, and since the incidents could not be given their proper setting he assumed that they had happened to him. In this case the defect of memory was a defect in the sense that previous occurrences were not properly located as to personality. The special incidents were suitably remembered, but the reference of them was erroneous.
Closely associated in character with the delusions which have just been described are others which the French call “déjà vu” and “dejà entendu.” These are conditions in which the individual experiencing them believes that he has had similar experiences in the past. In a perfectly new situation, in a place which he has never before visited, a person believes that he has been a visitor there at some previous time. Or words which are read in the newspaper or words that are heard are believed to be exactly the same as others which he has experienced in the past, not only with respect to the individual words or their combination, but also with respect to their context and their meaning as applied to him. These feelings of having already experienced such situations are frequently due to memory defects. But in these cases the memory defects are of quite a different character from those in the cases which have previously been described. In the condition of “déjà vu” ​it is probable that what takes place is that one or several elements in the present situation are like those which had been experienced in the past, but that the dissimilarities in the situations are not observed. The individual has a memory defect in that he parallels or identifies a complex present experience with a similar complex past experience, although in the present experience the number of elements which are the same as those in the past may not be very great. In other words, the present experience is deemed to be the same as that of the past because of the fact that the past is not accurately remembered and properly localized in time.
Throughout all of these delusions one may discover that, in general, there are two ways in which they arise. As far as can be determined, Southard points out, the patients take data which are erroneous, such as the lack of sensation (anesthesia) and interpret the lack of normal sensation in a normal manner, viz., lack of sensation means that the part is missing. By a normal individual a different interpretation may be made, but the delusional interpretation is, it should be understood, equally logical. We may conclude, therefore, that delusions are sometimes due to the fact that abnormal sensory conditions are appropriately and logically interpreted. On the other hand, these delusions may also arise because of abnormal or faulty methods of interpreting the data which are correctly received by the patient. Thus, the woman who experienced a pain due to pleurisy did not say “I have a pain in my chest,” but “I have been shot in the chest.” In every case it is not always possible to determine whether the delusions are due to elements of abnormal data or elements of abnormal reasoning. It is possible that in every case both of these elements are to be found. As a rule, in those who are not mentally unbalanced anesthesias and pains do not lead to delusional interpretations. When the sciatic nerve has been cut in an otherwise normal individual the lack of sensations which are normally received from the foot and leg does not lead to the interpretation that the foot or leg has been cut off or is missing. Experiences through other channels of sense are added and are combined to interpret the phenomena in a normal manner. The leg exists, but it is not felt. The lack of feeling does, however, imply non-existence and this conclusion is most direct. Correction of this interpretation because of sensations obtained from other sources (e.g., the eye) are indirect. It is perfectly logical for the man suddenly stricken blind to believe that it has suddenly become dark. It is only by an extension of experience and by the utilization of other means of arriving at a conclusion that the logical interpretation gives way to what may be termed a “normal” interpretation. The formation of delusions as the result of abnormal modes of interpretation is probably most frequent.