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A Lecture on the Preservation of Health

A Lecture on the Preservation of Health
Category: Health
Title: A Lecture on the Preservation of Health
Release Date: 2006-05-11
Type book: Text
Copyright Status: Public domain in the USA.
Date added: 25 March 2019
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The Project Gutenberg EBook of A Lecture on the Preservation of Health, byThomas Garnett, M.D.

This eBook is for the use of anyone anywhere at no cost and withalmost no restrictions whatsoever. You may copy it, give it away orre-use it under the terms of the Project Gutenberg License includedwith this eBook or online at www.gutenberg.org

Title: A Lecture on the Preservation of Health

Author: Thomas Garnett, M.D.

Release Date: May 11, 2006 [EBook #18376]

Language: English


Produced by R. L. Garnett


Professor of Natural Philosophy and Chemistry in the
Royal Institution of Great Britain &c.



     Such the reward of rude and sober life;
     Of labour such. By health the peasant's toil
     Is well repaid; if exercise were pain
     Indeed, and temperance pain. Armstrong.

(R. NOBLE, Printer, Old Bailey.)


Dear Sir,

THE first edition of this pamphlet having been introduced to theworld under the sanction of your name, I take the liberty ofprefixing it to the second; and am happy in having another publicopportunity of expressing my thanks for the high gratification andinstruction which I have received from the perusal of your medicaland philosophical works.

I am,Dear Sir,With much esteem,Your very obedient servant,


Royal Institution,April 8th, 1800.


Most medical gentlemen will, it is supposed, agree that the greaterpart of the numerous train of diseases to which their patients aresubject, have been brought on by improper conduct and imprudence.That this conduct often proceeds from ignorance of its bad effects,may be presumed; for though it cannot be denied that some personsare perfectly regardless with respect to their health, yet the greatmass of mankind are too sensible of the enjoyment and loss of thisgreatest of blessings, to run headlong into danger with their eyesopen.

It was with the hope of making the laws of life more generallyknown, and better understood, and from thence deducing such rulesfor the preservation of health, as would be evident to everycapacity, that the author was induced to deliver this lecture. Ithas been honoured with the attention of numerous audiences, in someof the most populous towns in England, where it has generally beenread for the benefit of charitable institutions.

The author flatters himself, that besides the benefit produced byhis humble endeavours to serve these institutions, those endeavourshave not totally failed in the grand object of preserving health;and with the hope that the influence of the precepts here given, maybe farther extended, he has concurred in the ideas of those who haveadvised the publication of this lecture.

It is to be feared, that notwithstanding all which can be done,disease will continue to be a heavy tax, which civilized societymust pay for its comforts; and the valetudinarian will often betempted to envy the savage the strength and soundness of hisconstitution. Much however may be done towards the prevention of anumber of diseases. If this lecture should contribute to theattainment of so desirable an end, it will afford the highestgratification to the author.

The first part of the lecture is the substance of an essay which wasread by the author before the Royal Medical Society of Edinburgh,intended as a defence of the general principles of the system of Dr.Brown, whose pupil he then was. It was, according to custom,transcribed into the books of the society, and the public have nowan opportunity of judging how far Dr. Girtanner, in his firstessay published in the Journal de Physique, about two years after,in which he gives the theory as his own, without the leastacknowledgment to the much injured and unfortunate author of theElementa Medicinae, has borrowed from this essay.

In public lectures, novelty is not to be expected, the principalobject of the lecturer being to place in a proper point of view,what has been before discovered. The author has therefore freelyavailed himself of the labours of others, particularly of thepopular publications of Dr. Beddoes, which he takes this opportunityof acknowledging.

This lecture is published almost verbatim as it was delivered. Onthis account the experiments mentioned are not minutely described,the reader being supposed to see them performed.

* * * * *


THE greatest blessing we enjoy is health, without it, wealth,honors, and every other consideration, would be insipid, and evenirksome; the preservation of this state therefore, naturallyconcerns us all. In this lecture, I shall not attempt to teach youto become your own physicians, for when the barriers of health areonce broken down, and disease has established itself, it requiresthe deepest attention, and an accurate acquaintance with theextensive science of medicine, to combat it; to attain thisknowledge demands the labour of years. But, a majority of thediseases to which we are subject, are the effects of our ownignorance or imprudence, and it is often very easy to prevent them;mere precepts however, have seldom much effect, unless the reasoningupon them be rendered evident; on this account, I shall firstendeavour, in as plain and easy a manner as possible, to explain toyou the laws by which life is governed; and when we see in whathealth consists, we shall be better enabled to take such methods asmay preserve it. Health is the easy and pleasant exercise of all thefunctions of the body and mind; and disease consists in the uneasyand disproportioned exercise of all, or some of the functions.

When dead matter acts upon dead matter, the only effects we perceiveare mechanical, or chemical; for though there may appear to be otherkinds of attraction, or repulsion, such as electric and magnetic,yet these come under the head of mechanical attraction, as producingmotion; we may therefore lay it down as a law, that when dead, orinanimate bodies act upon each other, no other than mechanical, orchemical effects are produced; that is, either motion, or thedecomposition, and new combination of their parts. If one ballstrike another, it communicates to it a certain quantity of motion,this is called mechanical action; and if a quantity of salt, orsugar, be put into water, the particles of the salt or sugar willseparate from each other, and join themselves to the particles ofthe water; the salt and water in these instances, are said to act oneach other chemically; and in all cases whatever, in whichinanimate, or dead bodies act on each other, the effects producedare, motion, or chemical attraction.

But, when dead matter acts on those bodies which we call living, theeffects are much different; let us take for example a very simpleinstance.—Snakes, at least some species of them, pass the winter ina torpid state, which has all the appearance of death; now heat, ifapplied to dead matter, will only produce motion, or chemicalcombination; but if it be applied to the snake, let us see what willbe the consequence; the reptile first begins to move, and opens itseyes and mouth; when the heat has been applied for some time, itcrawls about in search of food, and performs all the functions oflife. Here then, dead matter, when applied to a living body,produces living functions; for if the heat had not been applied, thesnake would have continued senseless, and apparently lifeless. Inmore perfect animals, the effects produced by the action of deadmatter on them, are more numerous, and are different in differentliving systems, but are in general the following—sense and motionin almost all animals, and in many the power of thinking, and otheraffections of the mind. The powers, or dead matters, which areapplied, and which produce these functions, are chiefly, heat, food,and air. The proof that these powers do produce the livingfunctions, is in my opinion a very convincing one, namely, that whentheir actions are suspended, the living functions cease; take away,for instance, heat, air, and food from animals, and they soon becomedead matter, and it is not necessary that an animal should bedeprived of all these to put a stop to the living functions; if anyone of them be taken away, the body sooner or later becomes deadmatter: it is found by experience, that if a man be deprived of air,he dies in about three or four minutes; for instance, if he beimmersed under water; if he be deprived of heat, or in other words,exposed to a very severe degree of cold, he likewise soon dies; orif he be deprived of food, his death is equally certain, though moreslow. It is sufficiently evident then, that the living functions areowing to the action of these external powers upon the body. What Ihave here said, is not confined to animals, but the living functionsof vegetables are likewise caused by the action of dead matter uponthem. The dead matters, which by their action produce thesefunctions, are principally heat, moisture, light, and air. Itclearly follows therefore, from what I have said, that living bodiesmust have some property different from dead matter, which rendersthem capable of being acted upon by these external powers, so as toproduce the living functions; for if they had not, the only effectswhich these powers could produce, would be mechanical, or chemical.Though we know not exactly in what this property consists, or in whatmanner it is acted on, yet we see, that when bodies are possessed ofit, they become capable of being acted upon by external powers, andthus the living functions are produced; we shall therefore call thisproperty excitability, and in using this term it is necessary tomention, that I mean only to express a fact, without the leastintention of pointing out the nature of that property whichdistinguishes living from dead matter, and in this we have theexample of the great Newton, who called the property which causesbodies in certain situations to approach each other, gravitation,without in the least hinting at its nature; yet, though he knew notwhat gravitation was, he investigated the laws by which bodies wereacted on by it, in the same manner, though we are ignorant ofexcitability, or the nature of that property which distinguishesliving from dead matter, we can investigate the laws by which deadmatter acts on living bodies through this medium. We know not whatmagnetic attraction is, and yet we can investigate its laws; thesame holds good with regard to electricity; if we ever should attaina knowledge of the nature of this property, it would make noalteration in the laws which we had before discovered.

I shall now proceed to the investigation of the laws by which theexcitability is acted on; but I must first define some terms whichit will be necessary to use, to avoid circumlocution, and at thesame time to give us more distinct ideas on the subject.

When the excitability is in such a state as to be very susceptible ofthe action of external powers, I shall call it abundant, oraccumulated; but when it is found not very capable of receivingtheir action, I shall say, it is deficient, or exhausted. Iwould not wish however, to have it thought, that by these terms Imean in the least to hint at the nature of excitability, nor thatit is really one while increased, and at another diminished inquantity, for the abstract question is in no shape considered; weknow not whether the excitability, or the vital principle, dependson a particular arrangement of matter, or from whatever cause it mayoriginate; by the terms here used, I mean only to say, that theexcitability is easily acted on when I call it abundant, oraccumulated; at other times the living body is with more difficultyexcited, and then I say, the vital principle is deficient, orexhausted.

The laws by which external powers act on living bodies, will, on acareful examination, be found to be the following—

First, when the powerful action of the exciting powers ceases forsome time, the excitability accumulates, or becomes more capable ofreceiving their action, and is more powerfully affected by them.

If we examine separately the different exciting powers, which act onthe body, we shall find abundant confirmation of this law. Let usfirst consider Light; if a person be kept in darkness

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