Part 2

With pleasure I take this opportunity of acknowledging how much the hints I receiv’d from the instructive lectures of my ingenious Preceptor Mr. Monro, contributed to this undertaking.

ESSAY

ON THE

Incubus, or Night-mare.

CHAP. I.

Of the history and the various opinions concerning the cause of this Disorder.

In order to convey a distinct idea of the subject of the following pages, I shall, according to the old custom of medical authors, begin with the etymology of it.

Altho’ we have reason to believe, as will afterwards appear, that this Disease was known long before the Greek language, yet, the earliest account we have of it, is from the Greek authors, who call’d it Εφιαλτης, and the Romans nam’d it Incubus, both which words partly express its effects.

In our language it is generally known by the name of the NIGHT-MARE; which strange term probably arose from superstitious notions which the British had, and perhaps still have, of it. How it first obtain’d this odd appellation, I never could learn, nor is it material to know, since that name is sufficient to distinguish it from every other Disease.

The Night-mare generally seizes people sleeping on their backs, and often begins with frightful dreams, which are soon succeeded by a difficult respiration, a violent oppression on the breast, and a total privation of voluntary motion. In this agony they sigh, groan, utter indistinct sounds, and remain in the jaws of death, till, by the utmost efforts of nature, or some external assistance, they escape out of that dreadful torpid state.

As soon as they shake off that vast oppression, and are able to move the body, they are affected with a strong Palpitation, great Anxiety, Languor, and Uneasiness; which symptoms gradually abate, and are succeeded by the pleasing reflection of having escap’d such imminent danger. All these symptoms I have often felt, and hope, that whoever has had, or may have, this Disease, will readily know it by this description, which I have not only taken from my own feelings, but from the observations of many of my acquaintances, who were also afflicted with it, and from the records of the antient observators.

Before I enter into an enquiry concerning the cause of this Disorder, or attempt to assign any one for it myself, I shall first take notice of the principal opinions that have been advanc’d to account for it, and examine how far they are confident with the laws of the animal œconomy; that the judicious reader may see how necessary further enquiries into the nature of this Disorder may be.

Doctor Willis says, That the Night-mare is owing to some incongruous matter which is mix’d with the Nervous Fluid in the Cerebellum. But, as he has not told us what this matter is, or how it is produced, we can afford it little credit in this enquiry; because plethoric persons, who abound with the purest and richest Blood, in whom such incongruous matter is suppos’d least to prevail, are most subject to this Disorder.

Bellini, who, in many other cases, is allow’d to be a pretty accurate theorist, was strangely mistaken in this, when he said, That the Night-mare is an imaginary Disease, and proceeds from the idea of some demon, which existed in the mind the day before.

This account is very unworthy a physician, and is a strong evidence that he never felt the heavy effects of this Disorder; otherwise he would have allow’d it to be a real Disease of the Body.

A metaphysician has laid great stress on this Disease, as an argument in defence of some of his wild opinions. He asserts, That it is owing to the operation of certains demons, which impose on, and torment, the mind in sleep.

This ingenious hint he took from Bellini, who probably stole it from Paracelsus’s doctrine of Archeus faber.

The ingenious Doctor Lower is the first author I met with, who observ’d the horizontal position of the Body, and assign’d it as a remote cause of this Disorder, but seems to attribute it immediately to a collection of Lymph in the fourth Ventricle of the Brain.

He says, “Si supine dormiant, Ventriculus ille quartus, Lympha nimium distensus, Medullam Oblongatam sua gravitate premit, ideoque fluxum liquidi Nervosi in Nervis cordi & respirationi inservientibus impedit.”

Perhaps he did not apply his first observation so well as might be expected from one of his abilities; for it seems needless to wait for a slow secretion of Lymph to produce this Disease, since, according to his own account, the return of the Blood from the Head, by the Jugular Veins, is in some measure prevented, and by that means a greater quantity of Blood than usual will be collected in all the vessels of the Brain; which might better answer his purpose, and more effectually obstruct the nervous influence. But before either of these causes could be removed by common methods, life would be at an end, and every fit of the Night-mare would be mortal; but that it often happens otherwise, many can testify. Doctor Lower seems to have founded this theory on the dissection of a Man who died of a Hydrocephalus, and not immediately of the Night-mare: hence that case is ill applied by Bonetus.

CHAP. II.

An enquiry concerning the real cause of the Night-mare.

Having mentioned the most remarkable opinions, that have occurr’d to me concerning the cause of this Disease, and shewn them all defective, I shall next consider several circumstances attending an horizontal position of the Body in sleep, in which alone this disease is felt; and endeavour from thence to investigate the real cause of it.

Sleep is the balmy anodyne of nature; and was intended, by the all-wise Author of our being, to ease the toils of the body, dispel the cares of the mind, and to repair the losses sustain’d by the fatigue of the day. In it we see every external stimulus remov’d, the Senses lock’d up, and every Muscle relax’d, except the Heart, the Sphincters, and those concern’d in respiration. Nutrition is then principally perform’d, and then only the Fluids glide equably through the Vessels.

As many of the voluntary Muscles are imployed in keeping the Body erect, ’tis necessary that the Body should be in an inclin’d or horizontal position, in order to relax them, and promote the salutary end of sleep. Accordingly we find, that most of the brute, as well as the human Species, chuse some easy posture of this kind to sleep in.

When the human Body lies horizontally, the Blood must flow in greater abundance to the Head; and with a greater momentum, cæteris paribus, through the Carotid and Vertebral Arteries, than when the Body stands erect; because the Blood, moving through these tubes in an horizontal direction, will not so much resist the force of the Heart, as when it ascends perpendicularly contrary to its own gravity.

No one, I presume, will doubt the truth of this proposition, who reflects, that it is much easier to move any spherical body on an horizontal plane, than to raise the same body up against a perpendicular wall.

Neither will it be denied, that the quantity as well as the velocity of Blood, flowing into the Carotid and Vertebral Arteries, is increas’d by the horizontal position of the Body, if it be consider’d, that these tubes (particularly the left Carotid) arise from, and proceed almost parallel with the axis of the Aorta, where the velocity of the Blood rushing out of the Heart is greatest. Whence it follows, from Sir Isaac Newton’s second general law of motion, and from a well known axiom in hydraulics, that these Arteries must receive more Blood in the same time, than any other branches of the Aorta of the same diameter.