ON INSTINCT. 



2lf 



equality in its own temperature with scarcely any variation : that in the case 

 of paralytic limbs it is the only power that continues vitality in them and pre- 

 serves them from corruption : that though not vascular itself, it is capable 

 by its own energy of producing new vessels out of its own substance, and 

 vessels, too, of every description, lymphatics, arteries, and even nerves ; and, 

 finally, that though, like the muscular fibre, it is capable of contracting upon 

 the application of a certain degree of appropriate stimulus, like the muscular 

 fibre, also, it is instantly exhausted of its vital power whenever such stimulus 

 is excessive ; and that the stroke of lightning which destroys the muscular 

 fibre and leaves it flaccid and incontractile, destroys likewise the blood, and 

 leaves it loose and incoagulable. 



In every organized system, then, whether animal or vegetable, and in every 

 part of such system, M^hether solid or fluid, we trace an evident proof of that 

 controlling and identifying power which physiologists have denominated, and 

 with much propriety, the principle of life. Of its cause and nature we know 

 no more than we do of the cause and nature of gravitation or magnetism. It 

 is neither essential mind nor essential matter ; it is neither passion nor sensa- 

 tion ; but, though unquestionably distinct from all these, is capable of com- 

 bining with any of them : it is possessed of its own book of laws, to which, 

 under the same circumstances, it adheres without the smallest deviation; 

 and its sole and uniform aim, whether acting generally or locally, is that of 

 health, preservation, or reproduction. The agency by which it operates is 

 that which we denominate or should denominate instinct, and the actions by 

 which its sole and uniform aim is accomplished are what we mean or should 

 mean by instinctive actions ; or, to speak somewhat more precisely, instinct 

 is the operation of the living principle, whenever manifestly directing its 

 operations to the health, preservation, or reproduction of a living frame, or 

 any part of such frame.* 



The law of instinct, then, is the law of the living principle : instinctive 

 actions are the actions of the living principle ; and either is that power which 

 characteristically distinguishes organized from unorganized matter, and per- 

 vades and regulates the former as gravitation pervades and regulates the lat- 

 ter, uniformly operating by definite means, in definite circumstances, to the 

 general welfare of the individual system or of its separate organs ; advancing 

 them to perfection, preserving them in it, or laying a foundation for their re- 

 production, as the nature of the case may require. It applies equally to plants 

 and to animals, and to every part of the plant as well as to every part of the 

 animal, so long as such part continues alive. f It is this which maintains from 

 age to age, with so much nicety and precision, the distinctive characters of dif- 

 ferent kinds and species ; which, as is noticed in a preceding study, carries off 

 the waste or worn out matter, supplies it with new,J and in a thousand in- 

 stances suggests the mode of cure, or even eifects the cure itself, in cases of 

 injury or disease. It is " the divinity that stirs within us" of Stahl ; the vis me- 

 dicatrix naturae of Hoffman and Cullen,^ and the physicians of our own day. 

 It is hence the strawberry travels from spot to spot, and the cod or the cuckoo, 

 with a wider range, from shore to shore, or from climate to climate. || 



* This Lecture was delivered January, 1813 ; and Mr. Keith on Tuesday, December 7, 1813, had a valu- 

 able paper read before the Linnaean Society, in which, like the present system, he opposes Mr. Knight's 

 hypothesis of gravitation as the cau^e of the peculiar stimulus a«d action of plants, and conceives that 

 " the direction of the plumule and radicle of plants must be reeved into vegetable instinct, precisely 

 analogous, and equally inexplicable with animal instinct."— See Tlffispson's Ann. of Philos. vol. iii. p. 71. 

 or No. 13. mjL 



t Mr. Knielit, while he seems desirous of resolving the principI^Bt vegetable action into centripetal 

 force, has shown liiat the sap of plants, as it exists in the leaves of p^ a bes and mint, and the leaves and 

 shoois of the vine, possesses what he cal!s organizable matter: and wvm} plunged in a moist and warm 

 soil will prodnre bulbs or roots more or less perlect, or at least, preserve and endeavour to extend life.— 

 Phil. Trans. 1816, p. 289. The whole, like the reproduction of polypes and worms from sections, ought 

 rather to be resolved into the common law of instinct, the aim of which is health, preservation, ©r repro- 

 duction : and hence the sap of plants seems as nmch alive as the blood of animals. 



t Series i. Lecture xiv. § First Lines, vol. i. p. 91. 105. 



II In conibrmity with the general principlesof his system. Dr. Darwin ascribes this extraordinary faculty 

 also to the power of reason. " It is [irobable," says he, " that emigrations were at first undertaken as acci- 

 dent directed, by the more adventurous of their species, and learned from one another like the discovtriea 

 <if num/eind in navigation."— Zoon. aticu xvi. 12. 



