too may the labour employed in keeping up productive powers; in preventing them from being destroyed or weakened by accident or disease. The labour of a physician or surgeon, when made use of by persons engaged in industry, must be regarded in the economy of society as a sacrifice incurred, to preserve from perishing by death or infirmity that portion of the productive resources of society which is fixed in the lives and bodily or mental powers of its productive members. To the individuals, indeed, this forms but a part, sometimes an imperceptible part, of the motives that induce them to submit to medical treatment: it is not principally from economical motives that persons have a limb amputated, or endeavour to be cured of a fever, though when they do so, there is generally sufficient inducement for it even on that score alone. This is, therefore, one of the cases of labour and outlay which, though conducive to production, yet not being incurred for that end, or for the sake of the returns arising from it, are out of the sphere of most of the general propositions which political economy has occasion to assert respecting productive labour: though, when society and not the individuals are considered, this labour and outlay must be regarded as part of the advance by which society effects its productive operations, and for which it is indemnified by the produce.
§ 8.Another kind of labour, usually classed as mental, but conducing to the ultimate product as directly, though not so immediately, as manual labour itself, is the labour of the inventors of industrial processes. I say, usually classed as mental, because in reality it is not exclusively so. All human exertion is compounded of some mental and some bodily elements. The stupidest hodman, who repeats from day to day the mechanical act of climbing a ladder, performs a function partly intellectual; so much so, indeed, that the most intelligent dog or elephant could not, probably, be taught to do it. The dullest human being, instructed beforehand, is
