The mental disorders which appear in the course of infectious diseases are brought about by the combined action of several factors: elevation of temperature, congestion of the nervous centers, and poisoning of these centers by microbic toxins. The most important factor appears to be the poisoning of the nervous centers.

One cannot fail to notice the striking clinical resemblance existing between toxic deliria and infectious deliria; indeed the resemblance is so close that without the somatic symptoms peculiar to each condition it would be difficult or even impossible to make the differentiation. Notes on such cases almost always describe the same symptoms, clouding of consciousness, confusion, numerous illusions and hallucinations, motor agitation.

Moreover, the infection itself, independently of hyperpyrexia and probably of any meningeal lesion, may cause grave mental disorders (infectious delirium proper) which can only be explained by a toxic action.

Febrile Delirium

In the mental disorders of febrile origin three degrees of intensity can be schematically distinguished.

In the slightest degree of intensity the disorder is limited to slight mental torpor and irritability.

In the second degree there is disturbance of ideation.

1 Klippel et Lopez. Du reve et du delire qui lui fait suite dans les infections aigues. Rev. de Psychiatrie, April, 1900. - Desvaux. Delire dans les maladies aigues. These de Paris, 1899.

The remarks of the patient become disconnected, and are characterized by a peculiar monotony suggestive of a fixed idea. Ten times in succession he will ask whether the cupboard is properly locked, or whether such and such a matter has been attended to, or whether some particular note has been duly paid. At the same time some illusions, chiefly affecting vision, make their appearance. It seems to the patient that someone is hiding behind the curtains, that the furniture in the room has assumed peculiar shapes. He does not recognize the voices of those about him and confounds them with one another. All these phenomena the patient;.s more or less conscious of. He realizes, either spontaneously or from the remarks made by those about him, that he is mistaken, "that he is raving, that he no longer knows what he is talking about." He is in a state of indefinable uneasiness and is apt to become somewhat restless, especially at night. He feels ill at ease in his bed, tosses from side to side, asks to get up.

Finally, in the third degree of intensity we have true delirium. This consists essentially in more or less profound clouding of consciousness combined with vague delusions, multiple psycho-sensory disorders, and motor excitement which is at times very marked.

The delirium is essentially variable and mobile, at time pleasant, at others painful; the psycho-sensory disturbances are of the combined form with a predominance of illusions and hallucinations of sight. Images and scenes follow one another as in a dream, of which they seem to be a continuation (dream delirium). The patient imagines he is in the country, in a theater, in a church; pompous processions march past him amidst the sounds of music and the perfume of flowers and censers; he converses with imaginary persons, defends himself against assassins, rejects a glass of milk offered him, thinking that it is poison. Often under the influence of his hallucinations he strikes at the air and attempts to get out into the street or to pass through the window, which he takes for the door.

However, as during a dream, the subject may by a sudden and energetic call be transported from his imaginary world into the real one. Such periods of lucidity are in general but transitory.

Often, chiefly in the beginning of all forms and through the entire course of the mild forms, the delirium disappears in the morning to reappear in the evening and to last during a portion of the night.

The prognosis depends less upon the intensity of the delirium than upon the physical symptoms which accompany it. As a rule all febrile affections complicated by intense delirium should be considered grave.

In fatal cases the delirium gradually subsides and coma replaces the excitement.

Febrile delirium, like acute alcoholic intoxication, is an excellent criterion for judging the resistance of the psychic organization: the greater the predisposition to mental disorders the more likely it is for delirium to occur under such circumstances. Like alcohol, microbic poisons and toxic products of the organism affect most readily minds the equilibrium of which is least stable and therefore most easily disturbed.

The treatment is that of the infectious disease. Strict watching is indicated. Cold baths are often very efficacious in relieving the mental disorders.

Infectious Delirium Proper

Kraepelin and Aschaffen-burg have described under the name of infectious delirium mental disorders which supervene in the course of an infection without the fever being particularly intense or even before any fever has appeared (Initial delirium).

Infectious delirium is met with chiefly in typhoid fever, in variola, and in typhus fever. The symptoms sometimes take the form of maniacal excitement, more often that Of an acute confusional state or of hallucinatory delirium.