360 



ON MATERIALISM 



It is high time to be more accurate, and to have both determinate words 

 and determinate ideas ; and it has been one object of this course of in- 

 struction to define what ought to be the real distinction between instinct, 

 sensation, and intelhgence. 



But let us ascend a step higher in the great scale of life ; let us quit 

 the vegetable for the animal kingdom. If I take the egg or grain of 

 a mustard-seed, and the egg of a silkworm, where is the chemist or phy- 

 siologist that will point out to me the diversity of their structure, or un- 

 fold the cause of those different faculties which they are to evince on future 

 developement and growth ? At present, so far as they appear to us, they 

 are equally common matter, actuated by the same common living principle, 

 directed to different ends. To give them developement and mature form, 

 we equally expose them to the operation of the sun and the atmosphere, 

 and, in the case of the mustard-seed, of moisture : and we are not con- 

 scious of exposing them to any thing else ; all which, again, so far as we 

 are acquainted with them, are nothing but matter in different states of mo- 

 dification. Yet the animal egg produces a new and a much higher power, 

 which we denominate sensation, while the vegetable egg produces nothing 

 of the kind. What is sensation, and from what quarter has it been de^ 

 rived ? Is it a mere property, or a distinct essence ? Is it material, or is 

 it immaterial ? 



This, also, has occasionally been called instinct, and been contemplated 

 as of instinctive energy. With equal confusion it has also been called or 

 contemplated as a property of mind. It is neither the one nor the other : 

 it is equally different from both. We trace, indeed, its immediate seat of 

 residence ; for we behold in the silk-worm a peculiar organ which does 

 not exist in the mustard-plant, and to which, and which alone, sensation 

 always attaches itself ; and to this organ we give the name of a nervous 

 system. But to become acquainted with the organ, in which sensation 

 resides, is no more to become acquainted with the essence of sensation 

 itself, than to know the principle of life because we know the general 

 figure of the individual animal or vegetable in which it inheres ; or than 

 to know what gravitation is because we see the matter which it actuates. 



As simple nerves, or a nervous cord, such as that of the spinal marrow, 

 is the proper organ of sensation or feeling, the gland of a brain, from 

 which the nervous cord usually, though not always, shoots, is the proper 

 organ of intelligence ; and as I had occasion to observe in a former study, 

 when lecturing upon the subject of the senses, the degree of intelligence 

 appears, in every instance we are acqujiinted with, to be proportioned^ 

 not, indeed, to the size of the brain as compared with that of the animal 

 to which it belongs, as was conjectured by Aristotle, and has been the 

 general belief almost to the present day, but as compared with the aggre- 

 gate bulk of nerves that issue from it.* The larger the brain and the 

 less the nerves, the higher and more comprehensive the inteUigence : the 

 smaller the brain and the larger the nerve, the duller and more con- 

 tracted. In man, of all anim als whatever, the brain is the largest, and 

 the nerves comparatively with its bulk the smallest: in the monkey tribes 

 it makes an approach to this proportion, but there is still a considerable 

 difference ; in birds a somewhat greater difference ; in amphibials the 

 brain is very small in proportion to the size of the nervous cord ; in fishes 

 it is a bulb not much larger than the nervous cord itself; in insects there 

 is no proper brain whatever ; the nervous cord that runs down the back 



♦ Ser. I. Lect. XV. 



