publishes here for the first time his methods for purifying yeast (the tartaric acid method, etc.), which were kept secret in his first smaller communications.

44

While the works of Pasteur on generatio æquivoca and on his fermentation theory caused prolonged contests, his attempts to introduce reform into technical fermentation very soon came to an end. His methods and suggestions were tested, but without giving successful results, as the most important thing, the pure yeast, was wanting. In Denmark, the Messrs. Jacobsen began experiments in the Old and New Carlsberg breweries shortly after Pasteur's work had appeared in 1876, using the methods there recommended for the purification of the yeast; but the results were not satisfactory. This was the case also in France and other countries. His Études sur la bière" are mentioned in the technical writings of that time with respect, but gradually become treated as something which had little to do with practice; they did not come into vital contact with the latter. The only upholder of Pasteur's work on technical fermentation is Velten, his co-worker on the subject of brewing. In the Revue universelle de la brasserie et malterie,” 1888, No. 742 and No. 743, he points out that it is the mixture of several different pure species of yeast which gives the beer the required flavour and bouquet. This is obtained, he asserts, according to Pasteur, by cultivation of the yeast in a cane sugar solution to which a little tartaric acid has been added, or in wort to which carbolic acid and alcohol have been added. As early as 1878 he had given, in the lectures which he delivered to the Congress at the International Exhibition in Paris, an exact description of this method, as Pasteur and he considered that the brewers should use it for the purification of their yeast. Velten published these lectures later under the title, "De la fabrication de la bière par le procédé Pasteur" (Revue universelle de la brasserie, 1881, No. 372). They are also to be found in the publications of the Congress. Duclaux also recommends Pasteur's above named methods in his "Chimie biologique," 1883, p. 301. As is mentioned in the introductory chapter, no one understood at that time the importance of the disease yeasts and their competition with the culture yeast; consequently also, it was unknown that Pasteur's method was specially favourable to the development of yeast diseases in beer. Thus in the above work Duclaux, in agreement with Pasteur, mentions (p. 618) only bacteria as the disease germs of beer. This, however, did not prevent him and other members of the French school from attempting later on to give quite a different interpretation to Études sur la bière". It became a regular practice to find in this work the new results produced by science after 1876 on the biology of yeast fungi and their use in technique. "Études sur la bière" abounds in contradictory opinions where the yeast fungus is treated,

without being decisive as to which is the right one. This is the case, e.g., in the question of the parent forms of yeast species (pages 155, 165, 177), and on top yeast and bottom yeast. (On p. 189 of the work cited, the view is expressed that a conversion of the one into the other does not take place, but on p. 333 the contrary is stated, viz., that the conversion of bottom yeast into top yeast can take place in breweries, a method even being described to prevent this.) By this means much confusion in the literature, and now and then little disputes, have been caused. The discussions of possibilities which occur in so many places in Pasteur's work enabled any one to find nearly always what he desired. Études sur la bière" was

66

not used as a scientific work, but rather as a Bible.

On the dispute which Hansen's work caused see p. 355.

XII.-TRAUBE, MORITZ: Theorie der Fermentwirkungen. Berlin, 1858.

XIII. DE SEYNES, JULES: Sur le Mycoderma vini. (Compt. rend., Tom. lxvii., 1868, p. 105.)

XIV.-REESS, MAX: Botanische Untersuchungen über die Alkoholgährungspilze. Leipzig, 1870.

XV. BREFELD, OSCAR: (1) Methoden zur Untersuchung der Pilze. (Ber. d. med.-phys. Ges. zu Würzburg, 1874; also in Landwirtsch. Jahrb., Bd. iv., 1875, p. 160.)

(2) Botanische Untersuchungen über Schimmelpilze. Heft 2 und 4, 1874 and 1881.

XVI.-LISTER, JOSEPH : On the Lactic Fermentation and its bearing on Pathology. (Trans. of the Path. Soc. of London, Vol. xxix., 1878, p. 445.)

XVII.—HOLZNER, GEORG Zymotechnische Rückblicke auf das Jahr 1877. (Zeitschr. f. d. ges. Brauw., 1878, p. 142.) XVIII. v. NÄGELI, CARL: Theorie der Gärung. München, 1879. XIX.-HANSEN, EMIL CHR.: (1) Contributions à la connaissance

des organismes qui peuvent se trouver dans la bière et le moût de bière et y vivre. (Compt. rend. des trav. du laborat. de Carlsberg, Tom. i., livr. ii., 1879, p. 49.)

In the above work Hansen communicates the preliminary investigations for his reforming researches published in the following years.

HANSEN, EMIL CHR.: (2) Recherches sur les organismes qui, à

différentes époques de l'année, se trouvent dans l'air, à Carlsberg et aux alentours, et qui peuvent se développer dans le moût de bière. (Ibid., Tom. i., livr. iv., 1882.)

In the note on p. 206 the chief features of Hansen's spore analysis are given. His first pure culture method is described on p. 212, and on p. 217 are described the first experiments on diseases in beer caused by fungi of alcoholic fermentation.

(3) Maladies provoquées dans la bière par des ferments alcooliques. (Ibid., Tom. ii., livr. ii., 1883, p. 52.)

(4) Les ascospores chez le genre Saccharomyces. Méthodes. (Ibid., Tom. ii., livr. ii., 1883, p. 28.)

(5) Méthodes pour obtenir des cultures pures de Saccharomyces et de microorganismes analogues. (Ibid., Tom. ii., livr. iv., 1886, p. 92.)

(6) Qu'est-ce que la levûre pure de M. Pasteur? (Ibid., tom. iii., livr. i., 1891, p. 24.)

The most important researches of Hansen are contained in the four works mentioned below.

(7) Recherches sur les organismes qui, à différentes époques de l'année, se trouvent dans l'air, à Carlsberg et aux alentours, et qui peuvent se développer dans le moût. de bière. (Compt. rend. des trav. du laborat, de Carlsberg, 1879, 1882.)

(8) Recherches sur la physiologie et la morphologie des ferments alcooliques. (Ibid., 1881, 1883, 1886, 1888, 1891, 1898, 1900, 1902.)

(9) Recherches sur les bactéries acétifiantes. (Compt. rend, des trav. du laborat. de Carlsberg, 1879, 1894, 1900.)

(10) Untersuchungen aus der Praxis der Gärungsindustrie.

The first edition of this work is given in Danish, with a résumé in French in the "Compt rend. des trav. du laborat. de Carlsberg," 1888, 1892. Of the more complete German edition (Oldenbourg,

Munich and Leipzig) there appeared: Part I., edition 1, 1888; edition 2, 1890; edition 3, 1895; Part II., 1892. The collected English edition appeared in 1896. (Spon, London and New York.)

The first to advocate Hansen's pure culture system in the literature was Carl Lintner, sen., who was then professor and director of the Royal Bavarian Agricultural Centralschule in Weihenstephan (Zeitschr. f. d. ges. Brauw., 1884, p. 245). Aubry at the same time introduced Hansen's innovations into the scientific brewing station at Munich. In his report for the year 1897 (p. 591 in the above journal), Will mentions that "the epoch-making ideas of Hansen have found a home and fostering ground in this station for more than a decade". "Our station," he adds, "was the only one for a long time which disseminated them among brewing circles on the Continent and gave them due recognition. The stormy period and the vigorous struggle is probably still in the memory of each of us, which was necessary to overcome the many prejudices which opposed the introduction of the pure cultivated yeast into practice, not only on the part of practical men, but also of eminent theorists, and to allay the misunderstandings which were always cropping up." Later on the acceptance became general.

also

In Denmark, Chr. Grönlund and Alfr. Jörgensen in particular advocated Hansen's reforming works, and the latter particularly has striven to obtain their general acceptance. (See his text-book "Die Microorganismen der Gärungsindustrie," 1-4 editions, 1886-1898; Centralbl. f. Bakt., Parasitenk. u. Infektionskr.," 2 Abt., 1897, p. 665, and finally the section: "Die Theorie der Gärung," in Thausing's "Malzbereitung und Bierfabrikation," 1898, p. 651, besides his numerous articles in the brewing journals.) In this connection may be named also the two jubilee reports which the Old and New Carlsberg breweries published in 1896 and 1897 respectively; likewise the articles published by Kjeldahl in the Nationaltidende," 15th May, 1887, and 10th November, 1897, by W. Johannsen in his textbook and E. Rostrup in the "Biographisk Lexikon ",

Particulars of the dispute which the pure culture system aroused are given in the "Wochenschr. f. Brauerei " and the "Zeitschr. f. ges. Brauw.," in the years following 1883. Velten and Duclaux have been mentioned on p. 352. The attacks were not always made in the most considerate manner, and they have been continued down to the present time. (On this point see J. Chr. Holm, "Hansen's Reinzuchtsystem in Frankreich, Centralbl. f. Bakt., Parasitenk. u. Infektionskr.," 2 Abt., 1899, p. 641, where still further references are given; they supplement the final chapter in Jörgensen's text-book, 1898.)

In the introduction to his " Mikroskopische Betriebskontrolle in den Gärungsgewerben," 1 Aufl., 1895; 2 Aufl., 1898, P. Lindner on

p. 10 writes appreciatively: "Hansen by the use of the pure culture becomes the reformer in the science of yeast organisms, as Koch was in that of bacteria". The object of his book, however, consists in substituting in several places other methods in place of those introduced by Hansen; methods, viz., which more resemble those of Koch. In it, he attacks several points in Hansen's work in that direction which have been defended by Alfr. Jörgensen and Will. The latter says (Zeitschr. f. d. ges. Brauw., 1899, p. 612): "The pioneer researches of Hansen have brought about a complete revolution in this direction. The extension of Pasteur's study of the organisms which produce diseases in beer, by Hansen, who showed that diseases are also produced by yeast species, and the building up of this theory by the latter investigator, his pupils and the zymo-technical laboratories, have advanced to such a point, that to-day we can with comparative quickness and certainty, by characteristic appearances, recognise all those organisms, in particular those yeasts, which are foreign to a normal yeast or fermentation and consequently also to a normal beer." Will and Jörgensen themselves have contributed. Among others, Prior's laboratory also took up Hansen's analytical methods. The latter depend in general on the study of important and characteristic physiological functions, but morphological characteristics were also included where this was possible. The same analysis can, of course, in many cases be performed in different ways. There is room enough for other methods besides those given by Hansen.

For illustrating the progress of the development it is instructive to go through various successive editions of textbooks and handbooks of the fermentation industries, e.g., such works as that of Thausing mentioned above. Even at the beginning of the eighties no mention is made of a reform with regard to the yeast question; but in the following years Hansen's ideas make themselves increasingly felt.

As regards the pure culture system in wine manufacture, see Wortmann's book, "Die Anwendung und Wirkung reiner Hefen in der Weinbereitung," Berlin, 1895. On the pure culture system in spirit and pressed yeast manufacture, see Delbrück and P. Lindner in the "Zeitschr. f. Spiritusindustrie," and 66 Wochenschr. f. Brauerei," 1892 and 1895.

Although a large part of Hansen's investigations deals with the study of species, and although they depart from new points of view and have given rise to important progress, systematic botany has hitherto paid little or no attention to them. Descriptive botanists repeated substantially the methods of description of Reess, and proceeded from the old fallacy that a microscopical investigation is sufficient to distinguish the systematic units from one another. It is still more unfortunate that such a doctrine is taught in more than