OF THE INSTINCTS OF NATURE IN

DISEASES.

NATURE has implanted in man, as in all other animals, a certain medical instinct, which is by no means to be disregarded. It laid the foundation of the whole practice of physic, and preceded the discovery of that science. There existed very skilful physicians before doctors were created, and these physicians were indiscriminately men and brutes. Nature, knowing the weakness of her creatures, could not possibly abandon them thus to their fate, for in that case they must soon have perished. The instinct of selfpreservation, with which she endowed them when she gave them life, was combined with a certain discrimination, which causes them to select and delight in things tending to promote their wellbeing, and to avoid and reject such as threaten them with danger and destruction. So deeply has Nature interwoven this secret feeling with the whole mechanism of the animal powers that they can scarcely ever develope themselves in their operations in any other manner than is consistent with our preservation. Too vivid a light, which would injure the eyes if suffered to shine into them, produces from its nature such an effect upon them that they must of necessity contract and thus exclude the redundant rays, without our having occasion to form previously any resolution on the subject, nay, even without our being able to avoid it if we would. When we inhale acrimonious vapours, which, if they were to remain in the lungs, would corrode their delicate texture, we are compelled, by the laws of the animal mechanism, to set in immediate motion all the machinery of respiration, in order to expel these vapours from the chest by an incessant coughing, and this effect takes place absolutely and even against our will. When there is in any of our vessels an obstruction of viscid humours, which by their rapid putrefaction might infect the whole frame, the sensitive machine is enjoined by the laws of Nature to inclose this

dangerous spot with an inflammation, which prevents the putrefaction of the obstructed humour, by converting it into a mild and innocent pus. If we attempt to perform an action that would do a dangerous violence to our limbs, pain is commissioned to warn us to desist, and in spite of our firmest resolution we are obliged to submit. When any of our passions exhausts by its vehemence the energies of our nature, that very exhaustion has the effect of reducing, cooling, and moderating it. If we carry the instinct of self-preservation to excess by means of artificial excitements; and are induced, for example, by the smel! of savoury viands to overload the stomach, this very gratification of the instinct produces a disgust, a loathing of more food; and if that cannot correct the fault, the stomach is forced to employ its own powers in a way contrary to its original destination, and to discharge the superfluous food by a vomiting, in which our resolution has no share. In short, all our actions and movements, as far as they are animal, are governed by this law of animal nature, and all tend to our preservation. All imaginations, conceptions, and desires, in as much as they are felt, excite in the machine peculiar movements, proportionate to their vivacity; and I know not whether it be more absurd to infer thence that the body of animals is actuated by an essence which obeys the law of their preservation, or that it accomplishes all this by the very same mechanical laws by which those machines move that are not animated by feelings. Of the two notions, that of Stahl is incontestably more rational and more consonant to nature than that of Des Cartes. Still both are erroneous; for I have shewn in the above instances, that the effects which by so wise an arrangement takes place in the animal economy, though they tend to its preservation, still do not proceed from the considerations of a rational essence which governs it, but that they in general either precede such considerations,

or happen in opposition to our own resolutions. In short, they take place according to the laws of animal mechanism, which are totally different from other known mechanical laws; and instead of explaining them by numberless errors, philosophers ought to have been content to have first made themselves acquainted with them. Thus the natural philosopher is not ashamed first to study the laws of physical phenomena, or the mechanic to observe the laws of mechanical effects, and then to explain such as he is capable of explaining, and to leave those which are incomprehensible to him where he

found them.

As, then, it appears from the preceding observations, that all animal machines receive the various impressions, which are either serviceable or detrimental to their preservation, in so decided a manner that they themselves labour for their well-being and against their destruction; so we thence deduce this incontestable inference, that, according to the laws of animal mechanism, every animal body must take in what is beneficial in a very different manner from what may be pernicious to it, and this is the foundation of the natural dietetic and medical instinct innate in all animals. The impression made by a poisonous vegetable on the senses of an animal, excites, even in the most hungry, an instantaneous nausea, on which account it loathes and rejects that vegetable. If its senses be impaired, and it should by mistake eat any poisonous food, no sooner has it reached the stomach than it compels that organ to exert its powers in a manner totally the reverse of its natural functions, in order to get rid of it by the shortest way; but, should its efforts fail, the effects of this poison on the animal body produce such movements as direct the senses and imagination to other things which are antidotes to it. In like manner the overloading of the stomach takes away the appetite from all animals, and if they then force themselves to take food, the most agreeable seems nauseous to them. This natural fasting is the cure of excessive repletion; and there is not a more cer

tain sign that the stomach is relieved of its burden, than the restoration of the regular appetite. The matter of fever, which heats the blood and approaches to putrefaction, has such an effect on the animal economy, that a violent thirst and a desire for acids, and

loathing of flesh and other aliments which have a tendency to putrefaction, take place. Are not all these real maxims implanted by nature in animals for the regulation of their diet and the cure of their diseases ?

Greater respect ought to be paid to this instinct in patients than is generally done, because it is the voice and an immediate effect of the wise providence of Nature. It is far from my intention to censure the subtle deductions of a well-directed ingenuity; but still I will take the liberty to observe, that our theories in general cannot be put together in the laboratory itself of Nature, but only behind the curtain, and that we ought to follow them if they stand the test; but that they certainly do not always stand the test, because we follow them whether right or wrong. How often have physicians had occasion to find fault with their predecessors for having kept their seat so pertinaciously in the saddle of their favourite theory as frequently to ride over Nature with their hobby! It is not long since patients afflicted with fever were not allowed a drop of drink, or persons in small-pox a breath of air, though the former were perishing of drought, and the latter by suffocation. In the sequel, physicians became convinced of the extreme absurdity of such excessive caution, and of the violence offered by it to Nature. A change in theories was the consequence, and we are now so unwilling to relinquish the modern ones and to admit the confutation of them by Nature, that we, on the contrary, oppose other instincts with as much obstinacy as our forefathers. Even when our theories are correct, they are inapplicable to particular cases; and were they to be correctly applied, yet the force of habit, and the sensibility of individuals, may sometimes counsel us against their application, when it is directly opposite to some powerful and

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permanent instinct of the patient. To such patients we ought to sacrifice the best theory, even when they desire pernicious things, that they may not entirely exhaust, in the conflict with the errors of habit, the feeble remains of their powers, which are nearly sinking under the disease. Solenander relates a fact which strikingly illustrates this subject. A peasant was seized with a violent fever, and every one was convinced that it was impossible for him to recover. The physician who attended him asked, if there was any thing that he had been particularly fond of which he should like to have. "Sir," replied he, "I have a mortal dislike to the food and the physic prescribed for me, as well as to the soft bed on which I am laid. For nineteen years I have lain upon straw in the open air, and eaten nothing better than black bread, cheese, and onions." The physician, considering this as the last will and testament of his patient, caused it to be duly executed. He was laid at night upon straw, had cold water given him to drink, and bread and cheese to eat; and next morning he was up by the fireside. Another physician of my acquaintance prescribed slops for a patient, who grew so much worse, that he directed him to take the strong beer to which he had been accustomed, and which invigorated and restored him. I could relate a thousand instances of this kind. The common man is well acquainted with them from repeated experience, and usually founds upon them his secret contempt of medicine. At the same time he judges inconsiderately. What does he know of the conditions and limitations that we must take such pains to discover before we dare either to sanction or to oppose the instincts of Nature in our patients? We are, indeed, obliged to do both; for either Nature and the physician are not infallible, or the most skilful physician is frequently incapable of distinguishing the desires originating in subtlety of understanding or obstinacy, from those dictated by the genuine animal instinct-the secret minister of Nature. There is no subject more deserving of close investigation than this.

Addison considered nothing as more mysterious than the instinct of animals, which sometimes rises far above rea son, and at others falls infinitely short of it. He could not venture to pronounce it a property of matter, neither could he, on account of its extraordinary effects, regard it as an attribute of an intelligence. He therefore looked upon it, like gravity in bodies, as an immediate impression of the First Mover, and as the Divine Power operating in its creatures.

There cannot be a more judicious comparison than this. As gravity imparts to a body the skill to pursue invariably the shortest way to the centre of the earth, without having the least consciousness of this action; so instinct directs animal bodies to their natural destinations, as though Nature herself had thoroughly instructed them in the secrets of her views; and thus they perform actions which are consonant with the laws of wisdom without knowing any thing of the matter. As Nature has endued physical bodies with peculiar properties, such as gravity, attraction, and the like, so has she bestowed others on animal bodies; and, if I may be allowed the expression, incorporated the most essential maxims of her wisdom into living machines, just as an artist makes an automaton that performs certain human actions, but in other respects can do no more than any other machine. The whole animal kingdom is full of instances of this sort. It is not out of respect, as every reader will easily believe, that a certain beetle described by naturalists, buries the dead moles and toads which it finds, but the instinct which teaches it to subsist upon those animals, and to deposit its eggs in them, impels it to this action. The pigeons which are trained to carry letters to distant places are not more sensible than other pigeons: nothing but the blind instinct to return to their young governs them in this proceeding. It is requisite that they should have left their young at the place to which they are to fly; and lest they should take a fancy to stop by the way to drink or to wash themselves, their feet are dipped at their departure in

vinegar. The Soland geese in St. Kilda steal, as Martin informs us, the grass out of one another's nests, not for the sake of stealing, but because they pick up grass wherever they find it, to form a soft depository for their eggs: and as these geese live together in flocks of many thousands, they find it every where in the nests of their companions. Highly as Ulloa extols the almost human caution and intelligence manifested by the mules in America in descending the lofty mountains, yet a closer examination will show that it is nothing but the fear of falling at the sight of the precipices, which occasions all their caution, without any farther consideration. If at Lima they stand with their legs wide apart when they hear a subterraneous rumbling, this proves nothing more than an habitual mechanical action acquired by frequent repetition; because when the earth shakes, they are obliged to assume a firmer position with their burdens, and they take the noise and the earthquake for one and the same thing, since the one invariably accompanies the other. Such is the real history of the supposed intelligence and cunning of animals. Nature must have known how far it was necessary for the skill which she conferred on animal bodies to extend, in order to the attainment of the purposes of self-preservation, self-defence, and the propagation of their kind. So much is certain, that all these instincts have their appointed limits beyond which no animal can go; and hence it is, that the animals, so long as they follow their instincts, perform actions of apparently astonishing intelligence, but in other respects are so stupid as not to manifest the slightest trace of cunning in their operations. A hen, whose providence and perseverance we admire, when she lays her eggs in some sequestered spot, where she sits on and turns them, and almost sacrificés herself in her attention to them, bestows the same pains on a lump of chalk which is put under her. She leads her chickens about that they may learn to scratch up the ground and to seek worms and insects. At the same time she will tread upon one of them, and affrighted at the cries which the

pain extorts from it, she clucks to warn and to soothe it; but yet she has not the sense to raise her foot and set it at liberty. A lobster will, with inconceivable dexterity snap off his leg when one of his fellows seizes it with his claw: but if you put one of his legs between his own claw, he will not have the sense to open his claw and to remove his leg, but breaks it off, as if there were no other method of releasing himself. The ostrich hatches her eggs, as it would appear, for the purpose of having young ostriches; she nevertheless quits them for every trifle, and leaves them to perish; nay, she will even break most of them herself, for the purpose of feeding with them the young ones which she already has. This bird has, moreover, the silly in-` stinct to swallow every thing that comes in its way, without discriminating, like other animals, whether it is hurtful to it or not. An ostrich swallowed, in Shaw's presence, several leaden bullets hot from the mould. It will greedily devour its own excrements and those of other birds, and of course manifests not the least choice in obeying the instinct of appetite. The crocodile would multiply with dangerous rapidity, were it not so stupid as to devour its own young, according to the testimony of Ulloa. Thus, too, the male tiger destroys its own species in its young; and it is observed of one of the bug family, that the female is obliged to use the greatest precaution to defend her eggs and her young from the male. The ascent and descent of larks are the result of an instinct implanted in those birds, which they follow without any consideration; for they do the very same over the sea as upon land, and hence frequently perish in the water. A thousand other examples of this kind might be adduced. They prove that these actions, which seem to manifest so much intelligence, are but the actions of a machine, adapted to certain particular purposes, and that to those purposes alone this apparent intelligence extends.

What can be inferred from all this, but that in the complicated relations in which an animal becomes involved during the whole course of its life, cases