[Footnote: 'Zeitschrift fur Analyt. Chemie,' 1881.] Hop flowers contain a great variety of different substances susceptible of extraction with ether, alcohol, and water, and distinguishable from one another by tests of a more or less complex character. The substances are: Ethereal oil, chlorophyl, hop tannin, phlobaphen, a wax-like substance, the sulphate, ammoniate, phosphate, citrate and malates of potash, arabine, a crystallized white and an amorphous brown resin, and a bitter principle. That the characteristic action of the hops is due to such of these constituents only as are of an organic nature is easy to understand; but up to the present we are in ignorance whether it is upon the oil, the wax, the resin, the tannin, the phlobaphen, or the bitter principle individually, or upon them all collectively, that the effect of the hops in brewing depends. It is the rule to judge the strength and goodness of hops by the amount of farina--the so-called lupuline; and as this contains the major portion of the active constituents of the hop, there is no doubt that approximately the amount of lupuline is a useful quantitative test. But here we are confronted by the question whether the lupuline is to be regarded as containing _all_ that is of any value in the hops and the leaves, the organic principles in which pass undetected under such a test, as supererogatory for brewers' purposes? Practical experience negatives any such conclusion. Consequently, we are justified in assuming that the concurrent development and the presence of the several organic principles--the oil, the wax, the bitter, the tannin, the phlobaphen, in the choicer sorts--are subject, within certain limits, to variations depending on skilled culture and careful drying, and that the aggregate of these principles has a certain attainable maximum in the finer sorts, under the most favorable conditions of culture, and another, lower maximum in less perfectly cultivated and wild sorts. The difference in the proportion of active organic substance in each sort must be determined by analysis. There then remains to be discovered which of the aforesaid substances plays the leading role in brewing, and also whether the presence of chlorophyl and inorganic salts in the hop extract influences or alters the results. That in brewing hops cannot be replaced by lupuline alone, even when the latter is employed in relatively large quantities is well known, as also that a considerable portion of the bitter principle of the hop is found in the floral leaves. Neither can the lupuline be regarded as the only active beer agent, as both the hop-tannin and the hop-resin serve to precipitate the albuminous matter, and clarify and preserve the beer.