The indirect causes of this disease are more numerous, and more frequent, though less suspected, than those which have been mentioned. The following diseases of the whole system appear to act indirectly in producing an internal dropsy of the brain.
1. Intermitting, remitting, and continual fevers. Of the effects of these fevers in inducing this disease, many cases are recorded by Lieutaud[47].
My former pupil, Dr. Woodhouse, has furnished me with a dissection, in which the disease was evidently the effect of the remitting fever. That state of continual fever which has been distinguished by the name of typhus, is often the remote cause of this disease. The languor and weakness in all the muscles of voluntary motion, the head-ach, the inclination to rest and sleep, and the disposition to be disturbed, or terrified by dreams, which are said to be the precursors of water in the brain, I believe are frequently symptoms of a typhus fever which terminates in an inflammation, or effusion of water in the brain. The history which is given of the typhus state of fever in children by Dr. Butter[48], seems to favour this opinion.
2. The rheumatism. Of this I have known two instances. Dr. Lettsom has recorded a case from the same cause[49]. The pains in the limbs, which are supposed to be the effect, I suspect are frequently the cause of the disease.
3. The pulmonary consumption. Of the connection of this disease with an internal dropsy of the brain, Dr. Percival has furnished us with the following communication[50]: “Mr. C——'s daughter, aged nine years, after labouring under the phthisis pulmonalis four months, was affected with unusual pains in her head. These rapidly increased, so as to occasion frequent screamings. The cough, which had before been extremely violent, and was attended with stitches in the breast, now abated, and in a few days ceased almost entirely. The pupils of the eyes became dilated, a strabismus ensued, and in about a week death put an end to her agonies. Whether this affection of the head arose from the effusion of water or of blood, is uncertain, but its influence on the state of the lungs is worthy of notice.” Dr. Quin likewise mentions a case from Dr. Cullen's private practice, in which an internal dropsy of the brain followed a pulmonary consumption. Lieutaud mentions three cases of the same kind[51], and two, in which it succeeded a catarrh[52].
4. Eruptive fevers. Dr. Odier informs us[53], that he had seen four cases in which it had followed the small-pox, measles, and scarlatina. Dr. Lettsom mentions a case in which it followed the small-pox[54], and I have seen one in which it was obviously the effects of debility induced upon the system by the measles.
5. Worms. Notwithstanding the discharge of worms gives no relief in this disease, yet there is good reason to believe, that it has, in some instances, been produced by them. The morbid action continues in the brain, as in other cases of disease, after the cause which induced it, has ceased to act upon the body.
6. From the dissections of Lieutaud, Quin, and others, it appears further, that the internal dropsy of the brain has been observed to succeed each of the following diseases, viz. the colic, palsy, melancholy, dysentery, dentition, insolation, and scrophula, also the sudden healing of old sores. I have seen two cases of it from the last cause, and one in which it was produced by the action of the vernal sun alone upon the system.
From the facts which have been enumerated, and from dissections to be mentioned hereafter, it appears, that the disease in its first stage is the effect of causes which produce a less degree of that morbid action in the brain which constitutes phrenitis, and that its second stage is the effect of a less degree of that effusion, which produces serous apoplexy in adults. The former partakes of the nature of the chronic inflammation of Dr. Cullen, and of the asthenic inflammation of Dr. Brown. I have taken the liberty to call it phrenicula, from its being a diminutive species or state of phrenitis. It bears the same relation to phrenitis, when it arises from indirect causes, which pneumonicula does to pneumony; and it is produced nearly in the same manner as the pulmonary consumption, by debilitating causes which act primarily on the whole system. The peculiar size and texture of the brain seem to invite the inflammation and effusions which follow debility, to that organ in childhood, just as the peculiar structure and situation of the lungs invite the same morbid phænomena to them, after the body has acquired its growth, in youth and middle life. In the latter stage which has been mentioned, the internal dropsy of the brain partakes of some of the properties of apoplexy. It differs from it in being the effect of a slow, instead of a sudden effusion of water or blood, and in being the effect of causes which are of an acute instead of a chronic nature. In persons advanced beyond middle life, who are affected by this disease, it approaches to the nature of the common apoplexy, by a speedy termination in life or death. Dr. Cullen has called it simply by the name of “apoplexia hydrocephalica.” I have preferred for its last stage the term of chronic apoplexy, for I believe with Dr. Quin, that it has no connection with a hydropic diathesis of the whole system. I am forced to adopt this opinion, from my having rarely seen it accompanied by dropsical effusions in other parts of the body, nor a general dropsy accompanied by an internal dropsy of the brain. No more occurs in this disease than takes place when hydrothorax follows an inflammation of the lungs, or when serous effusions follow an inflammation of the joints. I do not suppose that both inflammation and effusion always attend in this disease; on the contrary, dissections have shown some cases of inflammation, with little or no effusion, and some of effusion without inflammation. Perhaps this variety may have been produced by the different stages of the disease in which death and the inspection of the brain took place. Neither do I suppose, that the two stages which have been mentioned, always succeed each other in the common order of inflammation and effusion. In every case where the full tense, slow and intermitting pulse occurs, I believe there is inflammation; and as this state of the pulse occurs in most cases in the beginning of the disease, I suppose the inflammation, in most cases, to precede the effusion of water. I have met with only one case in which the slow and tense pulse was absent; and out of six dissections of patients whom I have lost by this disease, the brains of four of them exhibited marks of inflammation.