To what may we attribute the peculiarity of the beer as just described? It is probable that during our processes of purification some ferment had taken the place of the principal yeast. Commercial yeasts, even those with which the brewer is thoroughly satisfied, generally contain various ferments, which are maintained in their relative proportions, or very nearly so, by the uniform conditions under which work is carried on in a brewery; but these proportions, it is obvious, might be very seriously affected by any radical change in the conditions of growth. Footnote 82: Extract from a Note which I inserted in 1862 in the _Bulletin de la Société chimique_ of Paris. Footnote 83: Schützenberger, in his work on “Fermentation,” following Dr. de Vauréal. Paris, 1875, p. 278. [See pp. 61, 62 English version in International Scientific Series (H. S. King & Co., London, 1876). This appears to be the only reference to this subject in the English copy.—D. C. R.] Footnote 84: The principal result of Dr. Rees’ labours consists in the discovery of a sporulation peculiar to yeast cells, that is to say, to a formation in the interior of these cells, and under particular conditions—such as when the growth occurs on slices of cooked potatoes, carrots, &c.—of two, three, or four smaller cells, which, when placed in fermentable liquids, act like the germinating spores of ferments. The mother-cell may be regarded as an _ascus_, and the daughter-cells as _ascospores_, and so the genus _saccharomyces_ may be classified among the group of fungi termed _ascomycetes_. These facts have been frequently confirmed, notably by Dr. Engel, professor of the Faculty of Medicine, at Nancy. Previously to Dr. Rees’ discovery, M. de Seynes (_Comptes rendus_, t. lxvii., 1868) had described an endogenous formation of spores in _mycoderma vini_, particularly in the elongated cells, followed by the rupture of the mother-cell, and subsequent absorption of cell-walls and other contents after the issue of the endospores, which we have just termed _ascospores_. We ourselves had also previously called attention to those refractive corpuscles which appear amongst vibrios as probably being reproductive corpuscles, and we had likewise witnessed the reabsorption of the parts surrounding them. The plate on page 228 of our “Studies on the Silkworm Disease” represents the phenomena in question. Footnote 85: See _Comptes rendus de l’Académie des Sciences_, vol. lviii. p. 144. Footnote 86: The plates referred to in this paragraph were exhibited at a meeting of the Academy of Sciences, November 18, 1872, and commented upon by the perpetual secretary, M. Dumas. Footnote 87: