^40 



ON THE DISTINCTIVE CHARACTERS OF 



analogy to-sensation and perception as the latter does to crystallization 

 and chemical affinity. Instinct is the general faculty of the organized 

 mass as gravitation is of the unorganized mass ; sensation and perception 

 are peculiar powers or faculties appertaining to the first, as crystallization 

 and affinity are appertaining to the second ; they can only exist under 

 certain circumstances of the organized or unorganized matter to which 

 they respectively belong. 



This parallel, indeed, may be carried much farther. Gravitation dis- 

 covers itself under different modifications, different degrees of power, and 

 consequently different effects. Instinct evinces an equal diversity in all 

 these mstances. Gravitation belongs equally to the smallest and to the 

 largest portions of unorganized matter : instinct in like manner belongs 

 equally to the smallest and to the largest portions of organized matter ; 

 it exists alike in solids and in fluids ; in the whole frame, and in every part 

 of the frame ; in every organ, and in every part of every organ, so long 

 as the principle of life continues Sir Isaac Newton established the doc- 

 trine of gravitation, and overcame all objections to it chiefly by the modesty 

 with which he propounded and illustrated it. Without inquiring into the 

 nature of its essence, he contented himself with recognising it by its ope- 

 rations and laws. It is the aim ot the present study to follow this great ex- 

 ample ; and leaving all discussions concerning the essence of instinct or of 

 organized life, on which instinct is dependent, and which constitutes its 

 sphere, as matter constitutes the sphere of gravitation, to point out 

 nothing more than the nature of its action, and occasionally to catch a 

 glance at the laws by which it is regulated. 



From what has been already said, we see clearly that the power of 

 instinct runs equally through the limits of vegetable and animal life, and 

 consequently that instinct, sensation, and perception, whatever they con- 

 sist in, are powers or principles essentially different. Instinct is the com= 

 mon property of organized life in all its forms, but life itself is not neces- 

 sarily connected either with reason or sensation ; and it is of no small con- 

 sequence that we attend to this curious and extraordinary fact, the proofs 

 of which are abundantly in our own possession. The blood is alive, and 

 has all the common properties of life, as v/as very satisfactorily shown in 

 an antecedent lecture, from the experiments of Mr. John Hunter ; but 

 we all know that it possesses neither feeling nor intelligence ; the bones, 

 the cartilages, the cellular membrane, and the cuticle, are alive ; but, in a 

 state of health, they are equally destitute of both these properties, and 

 whether in health or disease, are always destitute of the latter. 



Sensation and perception, so far as we are capable of witnessing, can 

 only exist in appropriate organs, as nerves, or modifications of nerves, 

 which are the only known seat of the one, and the brain, or some modi- 

 fication of brain, which is the only known seat of the other. In the higher 

 classes of animals, as mammals, birds, amphibials, and fishes, the nerves 

 take their rise from the brain, or rather from some particular part of it. 

 But this is not an indispensable law of life ; for, in insects, we pieet with 

 nerves, but no brain ; and in most zoophyti(^ and many other tribes of 

 worms, with neither brain nor nerves. And hence, wherever these organs 

 or either of them are discoverable, it is consistent with right reason to 

 infer, that the faculty also exists to which they respectively give rise. But 

 on the contrary, where neither of these organs exist, as in plants, and a 

 multitude of the lowest tribes of animals, which in the zoological system 



