But this does not mean that physical labour is economic labour; far from it. The economic labour performed by the 10,000 H.U. in nowise consists of the reproduction of the same 10,000 H.U., wholly or partially, in this or that form. On the contrary, most of these are lost in the increased heat and radiation of the body, etc., and what remains available of them are the fertilising potentialities of the excrements. The economic labour which a man performs by the employment of these 10,000 H.U. consists rather in the fixation for a greater or less time of new H.U. radiated to him from the sun, which have only this labour connection with the first 10,000 H.U. Whether, however, the new quantity of H.U. fixated by the application of the 10,000 H.U. of daily nourishment reaches 5,000, 10,000, 20,000 or 1,000,000 H.U., depends solely on the degree of development attained by the means of production. This can only be represented arithmetically in the most primitive branches of production: hunting, fishing, cattle-raising, agriculture. In hunting and fishing new solar energy is not even fixated, only what has already been fixated is turned to use. At the same time it is obvious that, assuming the fisher or hunter to be normally nourished, the amount of albumen or fat he gets by hunting or fishing is independent of the amount of these foodstuffs which he consumes. In cattle raising, energy is fixated in the sense that vegetable matter, which would otherwise rapidly wither, decay and decompose, is systematically transformed into animal albumen, fat, skin, bones, etc., and therefore fixated for a longer time. Here the calculation is already complicated. Still more so in agriculture, where the energy value of the auxiliary materials, manures, etc., also enters into the calculation. In industry all calculation comes to an end: in most cases the work added to the product can no longer be expressed in H.U. If, for instance, this is still possible with a pound of yarn because its toughness and capacity for resistance can just, with a lot of fuss and trouble, be reduced to a mechanical formula, here already this appears as an utterly useless piece of pedantry, and in the case of a piece of unbleached cloth, still more in the case of bleached, dyed and printed cloth, becomes absurd. The energy value of a hammer, a screw or a needle calculated according to the cost of production is an impossible quantity. In my opinion it is absolutely impossible to try and express economic relations in physical magnitudes. What Podolinsky has entirely forgotten is that man as a worker is not merely a fixer of present solar heat but a still greater squanderer of past solar heat. The stores of energy, coal, ores, forests, etc., we succeed in squandering you know better than I. From this point of view even fishing and hunting appear not as the fixation of new sun heat but as the using up and incipient waste of solar energy already accumulated. Further: what man does deliberately by work, the plant does unconsciously. Plants--and this is an old story already--are the great absorbers and depositors of sun heat in a changed form. By work, therefore, in so far as it fixates sun heat (which in industry and elsewhere is by no means always the case) man succeeds in uniting the natural functions of the energy-consuming animal with those of the energy-collecting plant. Podolinsky has strayed away from his very valuable discovery into mistaken paths because he was trying to find in natural science a new proof of the truth of socialism, and has therefore confused physics and economics.
Letters: Marx-Engels Correspondence 1882