Introduction to Thelwall's Vitality Lecture

Thelwall, John. (1793) An essay towards a definition of animal vitality; read at the theatre, Guy's Hospital, January 26, 1793; in which several of the opinions of the celebrated John Hunter are examined and controverted. London: T. Rickaby.


Mr. President,

As my sole motive for becoming a member of this society was the pleasure I always derived from the enlightened conversation of gentlemen of the medical profession, and as I have hitherto attended to the science only as a matter of entertaining curiosity, and not as a pursuit to which I have any present intention of devoting myself, I might, perhaps, without encountering the censure of the candid and considerate, have endeavoured to excuse myself from the execution of a talk to which the nature of my pursuits must necessarily render me so inadequate. But, as I am no friend to privileges, and would have every member of society endure his proportion of the public burthens; and as, above all, I would wish to exclude the idle drone from the hive os science, I felt myself called upon to perform the part allotted by our institutions, and to give every gentleman that opportunity of canvassing and controverting my opinions, which, with respect to theirs, I have occasionally exercised myself.

I have discarded, there4fore, as far as possible, the timidity naturally attendant upon the many disadvantages under which I labour, and launching into a new and untried region, have brought my little tribute of physical knowledge, or rather speculation, to the general fund; confident only n the hope, that the smallness of its value will in some degree be compensated by the cheerfulness with which it is contributed.

My theory will no doubt be found, in many respects, defective, from the want of more general information in the sciences of anatomy and physiology; and may, perhaps be erroneous in others, from the misapprehension of scattered facts, imperfectly collected, without the concatenation of circumstances by which they might be elucidated and explained. But such as it is, I am sure the society would pardon its imperfections, if they knew the numerous avocations among which it has been digested, and the small proportion of time I have been enabled to devote to its composition.

I make these observations, not to abate the ardour of controversy, or restrain the keenness of investigation. It is from that ardour, from that eeness, and not from any vague conjectures in this essay, that edification is to be expected by the society and so far am I from wishing to shelter my hypothesis behind the screen of any personal consideration, that I should neither be displeased at being convinced that I am wrong, nor backward in acknowledging my conviction. Reputation is not to be expected from so transient an attention as I have been enabled to pay this subject; nor can there be any disgrace in the failure of an attempt, which is the result rather of necessity than of choice.

In short, candour of judgment, and not indulgence in investigation, is what I solicit from the society; and for that I shall not solicit in vain.

It is necessary, however, before I proceed to may subject, to premise one remark. I do not here profess to delineate a perfect system. I have entitled my paper an essay, and as such only I wish it to be considered. I shall not therefore be expected to demonstrate every proposition, or to draw out every part of my theory with amplitude and perspicuity.

This, I believe, is what has never yet been done; nor, from the limits of our present knowledge, can it rationally be expected of any hypothesis upon this subject. The anatomical physiologist himself is frequently left to wander in the regions of conjecture. The functions of almost every organ may be traced farther than the existence of such organs can be detected by the minutest enquiry; analogy, therefore, is often called upon to supply the place of demonstration; or the more easy expedient is appealed to, of passing over in silence what cannot be readily accounted for. Many of the conjectures, it is true, which the imperfection of the senses, or the deficiency of observation, had rendered necessary to professors, have gathered confidence from the great authorities by which they have been sanctioned: yet let it not be forgotten that it is not in the nature of authorities to change conjectures into proofs. Let us remember also, that reason is the greatest authority of all; and that when systems clash, and demonstrations are not to be had, we ought not to consider who is the author of this, or who of that opinion, but which it is that involves the fewest absurdities, or is best supported by analogy, and the correspondence of the general laws of nature.