lectures on the theory and practice of physic,

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Page 1: LECTURES ON THE THEORY AND PRACTICE OF PHYSIC,

248

sion on the nerve, and finding it to be a i

picure. Is there not jnst an equal diffi-culty in single hearing with two ears?single thinking with a double brain ? andthe tangible perception of a single objectwith impressions on thousands of cuta-neous nerves? Here again philosophershave confidently asserted that we na-

turally see double; that tonch graduallyteaches us that objects are single, andhabit at last makes us see them so. Here

again we have not a shadow of proof tosupport so strange an assertion, whilewe collect clear evidence from infants,cataract cases, and young animals, thatthey naturally see objects from the firstsingle. Here again we find that expe-rience’is of no use when an error is reallymade; in sensorial affections, accompa-nied with strabismus, in displacement ofnne globe, or by pushing one eye asidewith the finger, double vision is produced,and continues as long as the cause lasts,in spite of our perfect knowledge thatthe objects thus seen double are reallysingle. Further, we find that in the at-tentive exercise of vision, when we lookat objects, one eye only is employed,although both may be open, and appa-rently directed towards the object thusexamined. A familiar experiment provesthis : placing any object (a pencil) be-tween himself and a candle, let a personbring the pencil and flame into a line,with both eyes open; then let him closeone eye, if it is the weak eye, the flameand pencil are still seen in a line as be-fore ; if it is the strong eye, the flame ofthe candle seems to move aside, and isnow seen out of the line with the pencil.In a considerable majority of instances,the right is the strong eye, or the oneused for attentive vision.

LECTURESON THE

THEORY AND PRACTICE OF PHYSIC,

BY DR. CLUTTERBUCK.

Theatre, General Dispensary, Aldersgaie-street.

LECTURE III.

Gentlemen,AT my last lecture, I pointed out some

of the distinguishing characteristics oflife, and I mentioned, as one peculiarity,the chemical composition, not as to the ele-ments, for these are the same as those of

common matter; but the arrangement ofthem, their proportions, and the laws oftheir combination, are all different.

The second property, which I describedas distinguishing living from common mat.ter, is that peculiar arrangement of parts,called structure; easy to be perceived,yet not so easily defined ; as far, however,as we can form an idea of it, the structureof living animals may be said to be fibrousand tubniar; the tubes, or vessels, as theyare termed, carrying fluids, constantlymore or less in motion.The third property, which I spoke of,

was that of self-preservatiaya, or the powerof resisting external agents.Now these properties may be consider.

ed as merely passive; for living beingsare characterised by others, which are

comparatively active. I may illustratethis by reference to the seeds of plants,and the ova of animals. These will re.main for months, or even years, an.

changed, still retaining their vital prin.ciple ; as is proved, by their beingready to vegetate and grow, when theproper circumstances are applied. Thus,when heat and moisture are applied toseeds, they begin to vegetate; and thesame of the eggs of animals, which are

5equally vivified by the influence of heat.These more active properties I shall

now proceed to speak of more par.ticularly.

Of the Fourth Property of Life, viz. Sus-ceptibility of Impression.

Susceptibility of Impression is one of themost wonderful of the properties of life.It is the capabiiity of being influenced,and excited to action, by the applicationof certain agents or causes. It has beencalled, also, irritability and excitability,and may be considered as a simple kindof feeling, though unattended with con-sciousness. The only proof we have ofthe existence of this principle, is thechanges which parts undergo, in conse-

quence of certain applications being madeto them. This property exists univer.sally in all living beings,-plants, as wellas animals,-and in almost every part ofthem. The parts of animals which arethns susceptible of impression when ap-plications are made to them, are cailedirritable parts. Almost all parts are irtit-

able, either entire, or in their componentparts. Thus, though bones, cartilagea,and tendons, are not observed to haveany perceptible motion excited in themby irritation, yet the individual parts ofwhich they are composed, as blood.ves-sels, absorbents, &c., effect important

changes iu those structures, which are

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thus proved to be irritable, i. e. sus-

ceptible of impression.The applications or causes which make

an impression, and excite emotion, in

living beings, are termed stimuli, or ex-citing powers. The impressions thus

made, though followed by action, we arenot, in general, conscious of. Thus, thefood excites the stomach, and the bloodthe heart and vessels, to perform theirrespective actions, without our being atall sensible or conscious of such impres.sions being made. In the same way, themost important functions, those the mostessential to life, are carried on, withoutour being conscious of the impressionbeing made, or our knowing, by any par-ticular feeling, what is going on in thesystem.In the same way, the causes of disease

often act upon us insensibly ; and weknow nothing of their application, till theyhave produced their efft’cts, as in the caseof contagion, &c.

It is upon this principle also, namely,the susceptibility, irritability, or excita-bility of the body, that medicines gene-rally act, for we seldom feel their firstimpression, and only become sensible totheir more remote effects, as in the caseof bark, mercury, arsenic, &c.This susceptibility of impression, or

irritability, is greater or less, accordingto various circumstances. It is greaterin some parts than in others,—as thestomach compared with the skin. Theformer is open to a number of impressionswhich the latter is insensible to. Thusipecacuanha, taken into the stomach, pro-duces an impression of which we are notdistinctly conscious, but which is soon

followed by violent action, yet the samesubstance applied to the skin producesno effect. The susceptibility differs withage; it is greater in young persons thanin old ones; so that the same degree ofstimulus will produce a greater effect inthe former than in the latter. Hence,therefore, in the application of agents tothe body, we are not only to take into ac-count the force of the impression, but thedegree of susceptibility also.The susceptibility of impression is dif-

ferent in health and in disease. In somediseases, it is much increased : in others,:b is diminished; of the latter, we haveinstances in brain-affections.This property is greater in some indi.

viduals than in others ; this is to be re-membered in the administration of medi- I,cines. One person requires a double andtreble dose of the same substance, to pro-duce the same effect. Unfortunately,we have no certain means of judging ofthe degree of susceptibility possessed by

tifferent bodies. We give medicines to)roduce certain effects, but we are al-ways doubtful whether these effects willbe produced. Sometimes,from a previousknowledge of the individual, we are ena-)led to judge in some degree, but neverwithout doubt.Both when in excess and when deficient,

susceptibility of impression predisposes:o disease, though of different kinds.When in excess, it disposes to inilamma-:ion and spasm; when deficient, it is at-:ended with torpor and inaction, andtheir consequences. ’

It is influenced by medicines, and va-rious other things. Thus narcotics andtonics diminish irritability, while mer.

:nry, on the contrary, increases it. Heatand cold affect it in opposite ways; theformer increasing, the latter diminishingt. These effects are seen in the influ-ence of climate, not only on the humantody, but on all living beings,

Susceptibility of impression, or irrita-bility, seems even to differ in kind, as

well as in degree, in different beings, andin different parts, owing probably to thedifference in structure. Thus applica.tions, such as medicines and poisons, mayhave no influence on some animals, which,nevertheless, prove destructive to others.Hence also, one part is forcibly impressedby one agent, which another is scarcelyat all affected by. Thus carbonic acid,which, when inhaled into the lunge,quickly destroys life, by suspending thevital functions, acts, on the contrary, Ma cordial in the stomach, and mvtgm atet,For a time, the whole system. So it iswith different kinds of animals. An agentwhich on one will act violeutly may pro.duce no effect upon another. Manythings, which operate mildly upon humansubjects, produce a contrary- effect onanimals. For instance, oil of turpentinehas no great power of stimulating thehuman skin; but that the horse is vel ysusceptible of the impression of this agent,and very violent inflammation is quicklyproduced by it. It is on this account,that in experementing on different ani.mals, we are not to conclude that thesame effect will follow on one,as on au-other tribe. Generally speaking, the su=-ceptibility of the horse is much less thanthat of man ; but the fact above mention-ed constitutes one of those exceptionswhich prevent our relying too much onanalogy.We have the same evidence of plants

possessing this principle of susceptibility,or irritability, or simple feeling, that wehave of animals ; namely, the c7tang-eswhich follow the application of stimuli tothem; and which, being the result of

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movements that are spontaneous,’ andnot mechanical merely, prove, that such’applications were, in some way, felt orperceived by them:

Fifth, of the Mobility of Living Beings.

Mobility, or the.power of m -oving spon-taneously, independent of mechanical im-pulse,. is another of the most striking andessential properties of life. Motion, inliving beings, is termed action, as beingspontaneous, and not passive. As far ascan be perceived, motion in living beingsis effected by contraction or shorteningof fibres; and, therefore, it has beensaid, " all action is contraction." Thekind of motion here alluded to, whichis characteristic of life, and therefore be-longs to all living beings, is performedinvoluntarily, and without consciousness.It is termed involuntary motion, to dis-tinguish it from another kind of motionperformed by animals, and not by plants,and which is called voluntary motion.The laws of motion, in animated beings,are quite different from those of inani-mate bedies, which are mechanical or

chemical merely, or dependant upon someother principle different from that oflife.

All part.. of ic body appear to be

"npable of Dotion, either in their entirestate, or in their component parts indi-vidually, Thus, though an entire bone isincapable of motion, the component partsnfthe bone, viz. its blood-vessels and ab-sorbents move or act, and changes ensuein consequence.The degree or quantity of motion in

living bodies, differs according to the na-ture and structure of the part, and itsrelative magnitude. Thus, in the largevoluntary muscles of the human body, inthe heart, and in the intestinal canal, themotion is easily perceived. Whereas, inall the smaller blood vessels, in the ab-sorbents, in the secretory vessels, &c.,’the motion is quite imperceptible, andonly proved to have taken place by thechanges which are constantly going on.

-lr2-itability and mobility always appearto accompany each other. It couldbe of no use that a part were capable offeeling an impression, if no change re-

sulted from it; that is, if it were inca-

pable of moving.Motion in living beings does not appear

in any case to be absolutely spontaneous,but to be always the result of some ex-

citing cause or stimulus. Thus the seedsof a plant, when dry, remain unchangedfor months, or even ages, unless meistureand a certain degree of heat are appliedto them. These are the stimuli, which

excite motion or action in the seeds ; theresult of which motion is vegetation or

growth. So also the egg in animals, con-tinueswithout alteration for an indefinitelength of time, till the stimulus of heatis applied to it, when it begins to move oract, and its parts to be developed into a

perfect animal. In both cases, the seedand the egg, which may be consideredanalogous beings, retain their living prin-

ciple, or, in other words, are alive; butcontinue inactive for want of the necessary stimulus. The only object ot the vitaiprinciple existing in them, is to preservethem for a time unchanged, against theinfluence of external agents. Hence weconclude, that life may exist in a passive

’ state ; and that action is always the resultof some stimulus, and consequently isliable to vary, according to the degree’ and nature of the stimulus applied.

The causes of involuntary motion, (orstimuli,) ia living beings, are almost in-, finitelv various. Some excite motion iu. one part but not in others ; as light to, the M’M, bnt not to any other part. Some- again seem capable of influencing every

part, as lteat and electricity.

t Involuntary motion may be excited inanimals by iclcas of the mind; of which

’ an example is afforded in the act of’ blushing, in the human subject,-in the- palpitation of the ’heart observable ia

s many animals, and in many other cases.’ Almost all the motions that ar imme-- diately essential to life in animals, equally: with the movements that take place in

plants, are involuntary; as the circulationa of the blood, absorption, secretion, di·

gestion, and many others, over which wehave no control.: The applications which produce invo<lun"tary motions are not ill general felt;’ nor are we conscious of such movementstaking place. Thus, as we before stated,- we do not feel the impulse of the blood9 on the heart, nor of the food on theI stomach, &c. nor are we conscious of tiie&middot; movements they excite ; and so pf others.

In diseases, however, it may be otherwise;as we often then feel painfully the pul-

I sations of the heart and arteries, or of thef action of the stomach or intestinal canal.Thus, also, in fevers, in which the brain

is in a diseased state, the throbbing ofthe arteries in the head, is often dreadfully

felt.

I shall now mention some of the lawswhich regulate involuntary motion inliving beings.

The degree of motion, or action, takingplace in living beings, is in a compoundratio of the force of the stimulus applied,

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the susceptibility of the body, and the

strength, or power of acting, which it

possesses. These are very variable, as isconsequently the effect. If the suscepti-bility be natural, and the power of acting,or strength, in the due degree,&mdash;then,stimuli applied in the proper degree, pro.duce healthy action. If either the degreeof stimulus applied, or the susceptibilityis changed, disordered action will be theresult. If the disposition, or irritability,be stronger than ordinary, then the effectof stimuli will be heightened. This isobserved in what we call irritable subjects,and irritable parts ; where slight stimuliproduce violent movements ; as in infants,who are greatly disordered by slightirritations. The reverse occurs wherethe disposition, i. e. the susceptibility orirritability, is deficient ; stimuli then pro-duce comparatively little effect, as in oldagf. This indisposition to act, or the wantof iriitability, may be connate, or it maybe the effect of disease. If natural, itis attended with a greater exemptionfrom disease, the subject being less rea-dily influenced by the various causes ofdisease. And disease, when it arisesin such, will be of a less activecharacter. This want of irritability is

generally discovered in the action of theheart, which is slow, and of course ren-ders the pulse slow also. Now, when thelungs become diseased in persons whohave naturally a slow pulse, the progressof the disease is less rapid, and vice versa.The general state of irritability is, how-,ever, not always to be judged of by thepulae. Deficient irritability in the gene-ral system is sometimes the result ofdisease or pressure on the brain,; in con-sequence of which the irritabilitv of theheart and intestinal canal, and various.other parts, is lessened ; and then theaction of these organs is diminished. I

The degree, or at least the continuanceof motion, is according to the power of I,acting, which is not the same thing withthe disposition. The power of acting inanimals.is expressed by the term strength.The dispos;tion to act, and the power to doso, may correspond or otherwise. If thedisposition to act, or irritability, and thePower of acting, or strength, are bothconsiderable, then stimuli, or the cause ofaction, produce a great and durableeffect. This occurs in young and vigoroussubjects, in whom diseases -are readilyexcited, and when excited are aptto proceed with violence. On the otherhand, if these properties are both defi-cient, then stimuli produce but little effect.Such a state of system is often observedin advanced life, where disease is less

readily excited, and when excited, is com-monly not violent, but long continued.The disposition may be strong, but thepower to act weak ; in this case, stimuliwill produce a considerable effect, butttwill be of short duration. This is thecase with infants, and in subjects calledirritable ; where slight impressions readilyexcite disease, which may be violent, butcommonly soon terminates. Weak per-sons are also often irritable, and arethereby very prone to disease, The dis-position to act may be moderate, and thepower of acting, or strength, at the sametime considerable. In this case, the va-rious functions of the body will be carriedon steadily and vigorously, and not beeasily disturbed by any of the causes ofdisease. Such a state of things is observedin healthy subjects, at the middleperiods of life, when the body is com-monly the most exempt from disease.

These differences in the constitution ofindividuals have great influence in ino-difying the character of diseases, whenthey occur; as well as on the liability tothem. They answer nearly to the termtemperament, employed by the ancients todenote certain constitutional pecniiari-ties. We can generally judge prettyaccurately of the strength of the stimulusor exciting cause, applied ’to the body’;but we can seldom estimate correctlyeither the susceptibility of impression, prthe power of acting; and, therefore, weare unable to predict, the effect that villfollow any particular application. Henfe,there is great uncertainty, with respectto the action of the causes of disease,and likewise as to the effect of remediesi

There are not only great differencesbetween different individaals, in regardto susceptibility and power of acting, butequal differences exist in the same indi-vidual in the different parts of the body.Some parts are more irritable than others,consequently, more readily e..:::::ite’ todisease. It may be the lungs, or thebrain, or the ligamentous structure-; andthen the individual becomes more liableto diseases of those particular parts thanof others. Such predisposition to certaindiseases often pervades whole families,and these diseases are then said to behereditary in such ; but it is only the dis,position to disease that ; hereditary,, andnot the actual disease.