One may “read” the heart and the vascular system as a pumping contrivance, and the osseous system and its joints as an arrangement of levers. One may reckon in heat-units the nutrition-values taken in and given off, and equilibrate them with tolerable success, as can also be done with a calorimeter; that is to say, one can “read” the living organism in accordance with the formula of the law of the conservation of energy. But nothing thereby is gained that is of the slightest assistance towards a comprehension of the _actual_ energies at work in all these functions, except in so far as to the genuine thinker all this makes more vital and pressing the question as to what precisely that wonderful something is which pulls the strings. And if one school of science would like to make us believe that on the basis of an ever-increasing facility in “reading” the organism mechanically the question as to actuating energies may in the end be completely disposed of, as referring to quantities so minute as to be negligible, it need not be taken seriously; it only resembles a man who would account for the revolution of a wheel solely from the shape and texture of the wood. That which along with the results of physiological chemistry helped towards the overthrow of the mechanical view, was the new tendency in therapeutics--serum therapeutics, to wit--which, put briefly, amounts to a working out of specific affinities between the living organism and certain organic substances. As the physiological chemist was forced to note that he had fallen out of the realm of crude but easily-handled quantities into the realm of unaccountable qualities--that is, out of re-actuality into actuality--so was it with the experimenter in these specific remedies. One was obliged to take note that in this field the grossly quantitative according to mass and weight no longer went for anything. Ehrlich calls the antitoxins “magic bullets” which hit their mark _immediately_. Here it is no longer a question of the mere more or less by which one has hitherto been accustomed to gauge effects, but of an attunement more or less fine and delicate. In short, one has forced one’s way into the domain of actual energies and seeks gropingly after one or another method of accommodation. For the quantitative position may not be abandoned entirely if one would remain scientific. One must be able to measure. Actual energies, however, do not admit of being measured by dead material. They are only to be measured through themselves, _i.e._ through their working.