The influence of hallucinations upon the will depends upon the state of the judgment and of the affectivity. If the judgment is sound, if the hallucinations are looked upon as pathological phenomena, they give rise to no reaction; and the same is the case when they make no impression upon the emotions.

But when they are accepted by the patient as real perceptions and influence strongly the emotional state, hallucinations, on the contrary, govern the will to a very considerable extent and prompt the patient to defend himself against the ill-treatment of which he believes himself to be the object or to obey the commands which are given him (imperative hallucinations). Hence the frequency of violent and criminal acts committed by the insane, and the well-known axiom in psychiatry according to which all subjects of hallucinations are dangerous patients. Revington has found, from a study of forty-nine cases of homicide committed by insane patients, that in most instances the murder resulted from a hallucination.1

The reactions caused by hallucinations are often abrupt, unreasonable, and of an impulsive character, especially in the feeble-minded and in patients with profound clouding of consciousness (delirium tremens, epileptic delirium). But they may also show all the evidences of careful premeditation. Certain persecuted patients, exasperated by their painful hallucinations, prepare their vengeance with infinite precaution.

The influence of hallucinations upon the will is often so powerful that nothing can combat it, neither the sense of duty, nor the love of family, nor even the instinct of self-preservation. A patient passing near a river heard a voice tell him: "Throw yourself into the water." He obeyed without hesitation, and to justify himself declared simply: "They told me to do it; I was forced to obey."

Combined Hallucinations

Sometimes hallucinations affect but one sense. Such are the hallucinations of hearing at the beginning of systematized delusional states. Generally, however, the pathological disorder affects several senses, the different hallucinations either following one another, or existing together without any correlation, or combining themselves and producing complex scenes either of a fantastic aspect or analogous to real life. In the latter case they bear the name of combined hallucinations. The patient sees imaginary persons, hears them speak, feels the blows that they inflict upon him, makes efforts to reject the poisonous substances which they force into his mouth, etc. This state, closely related to dreams, is always accompanied by marked clouding of consciousness.

1 Revington. Mental Conditions Resulting in Homicide. The Journ. of Ment. Sc, April, 1902.

Diagnosis Of Hallucinations

Two possibilities may present themselves: (1) the patient directly informs the physician about his condition; (2) he gives no information whatever, either because of his reticence or because of his intellectual obtuseness.

In the first case the diagnosis of hallucinations is generally easy. It is necessary, however, to ascertain that the pathological phenomenon is really a hallucination, and not an illusion; in other words, that it is a perception without an object, and not an inaccurate perception. Only a detailed examination of the circumstances under which the phenomenon shows itself may prevent an error; it is very difficult indeed when a subject hears himself being called a thief in the midst of thousands of street noises, to decide whether he experiences a hallucination or an illusion. The certainty is, on the other hand, much greater when the morbid perception occurs in absolute silence, as during the night.

In the second case the diagnosis must be made without the assistance of the patient, or even in spite of his denials. It must be based only upon the patient's attitudes, movements, and at times upon the means of defense to which he resorts and which vary according to the sense affected. The ear turned for some time in a certain direction, the eyes fixed or following a definite line without there being any real object to attract them, the ears stuffed with foreign bodies, evidences of strong emotions, an expression of fear, etc., lead to the presumption of the existence of hallucinations. I say presumption because the external signs do not enable us to establish with certainty the patient's state of consciousness. Over-refined psychological analyses are to be mistrusted if one is to avoid unwarranted conclusions which would render the diagnosis and prognosis faulty.

Relations Between Hallucinations And Other Mental Disorders

What position do hallucinations occupy in the genesis of the psychoses? Are they primary or secondary?

It is not impossible that at times, notably in the intoxications and in cases of localized lesion, hallucinations appear first and are the cause of the other mental disturbances which follow. In practice, however, such cases occur but rarely. A careful and complete history almost always shows that the hallucinations are preceded by other symptoms: depression, intellectual obtuseness, clouding of consciousness, delusions, etc.

Indeed it is difficult to conceive of one or more hallucinations appearing in a person free from all other mental trouble, without their being at once corrected by the judgment aided by the other senses. On the other hand it is quite intelligible that imaginary perceptions may exercise an influence upon the attention, the emotions, the judgment, and the will, if they are but the reflection or the realization of the patient's preoccupations and morbid ideas, that is to say, if they are secondary. The melancholiac who believes himself guilty of a crime sees and hears the police officers who are coming to arrest him. The paranoiac who believes himself to be exposed to the malevolence of his imaginary enemies hears their voices insulting him. The general paralytic with pleasing and expansive delusions experiences pleasant sensations. Hallucinations are, then, an expression, and not a cause, of delusions; and that is why they harmonize so perfectly with the mental state of the subject.

Some psychiatrists l have described a hallucinatory delirium as a distinct morbid entity the essential features of which are the multiplicity and the primary character of the hallucinations. If the idea which we attempted to convey above is correct, hallucinations, never or almost never being primary, cannot form the essential and exclusive feature of an affection, and hallucinatory delirium cannot retain its autonomy. For this reason most authors classify such cases with confusional psychoses, general paralysis, dementia praecox, and toxic psychoses.

General Etiology Of Hallucinations

On this subject we possess but very incomplete information.

Hallucinations appear readily in states of impaired consciousness, as epileptic delirium and the toxic psychoses. The hallucinations which precede sleep in certain nervous subjects are most frequently of the conscious type and are to be attributed to weakening of consciousness.

Hallucinations are very apt to appear in the absence of real sensations - those of hearing during silence and those of vision in darkness. This explains why isolation in prison cells predisposes to hallucinatory psychoses (Kirn, Rudin).2

In some instances hallucinations are produced in a somewhat automatic manner, at the occasion of some definite impression. One patient felt a taste of sulphur in his mouth whenever the name of one of his persecutors was uttered in his presence. Such hallucinations have been described by Kahlbaum under the name of reflex hallucinations.

Hallucinations may depend to a certain extent upon a peripheral excitation either of the sensory organ itself or of the conducting nerve. They are in such cases frequently unilateral. "Max Busch has brought about a notable improvement in the mental condition of a patient who had auditory hallucinations which were most marked on the left side, by treating his otitis media with perforation of the drum membrane, which he had contracted during childhood." 1 Visual hallucinations have been observed to appear as the result of ocular lesions, such as cataract, and to disappear under appropriate treatment. These peripheral lesions are, so to speak, but a pretext for the hallucinations, and are not to be considered as their true cause. The cause is to be looked for in a special state of morbid irritability of the centers of perception which causes them to react by hallucinatory phenomena to abnormal peripheral excitation.2 Hallucinations sometimes occur in cases in which the corresponding sensory function has been lost completely.

Thus auditory hallucinations may be associated with total deafness, unilateral or bilateral.

1 Farnarier. La psychose hallucinatoire, Paris, 1899.

2 Rudin. Eine Form akuten hallucinatorischen Verfolgungswahns in der Haft, etc. Allg. Zeitschr. f. Psychiat., 1903.

Peripheral hallucinations are very analogous to Liep-mann's phenomenon: if in a convalescent alcoholic slight pressure is made upon the eyeballs, hallucinations are sometimes induced, even when the subject does not any more experience them spontaneously. The peripheral excitation transmits to the brain nothing but a nervous discharge, the clinical expression of which is the hallucination. The s'act that a great many patients present very grave and old standing lesions of the sensory organs without having any hallucinations is also evidence to prove that these affections are of but secondary importance in the causation of psychosensory disorders.

Finally, hallucinations may be induced by suggestion. Sometimes it suffices merely to fix the attention of the patient upon a certain point for him to discover imaginary objects, persons, or forms. Such is frequently the case in toxic states, notably alcoholism and cocainism, also in certain dementias. In an observation kindly communicated by Thivet, a patient read whole words upon a blank surface that was presented to him.

1 Quoted by Legay. Essai sur les rapports de Vorgane auditif avec les hallucinations de I'ou'ie. These de Paris, 1898, p. 25.

2 Joffroy. Les hallucinations unilaterales. Arch, de neurol., 1896, No. 2. - Mariani. Un cas d'hallucination unilaterale. Riforma raedica, 1899, Nos. 30 and 31.