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aceti, p. 336 ; Bact. Pasteurianum, p. 337 ; Bact. Küt-
In this text book the author has endeavoured to give a review of the biology of fermentation organisms in relation to the use of these organisms in fermentation industries, and especially in the manufacture of beer. In spite of this limitation, however, the contents are of very varied character, and branch off in different directions. The book is not a text-book of the chemistry of fermentation or of technical fermentation in the ordinary sense of the term.
For the high degree of development to which our knowledge of the fermentation organisms has attained we are indebted to a large number of investigators whose work has been steadily progressing for many years. To understand the development of our science up to the present day, let us, in what follows, glance back along the path traversed, and note its turning points, each one of which has been productive of practical results, the value of which is recognised at the present day. The beginning was, of course, first made when the microscope came into use. This apparatus, so indispensable for the examination of fermentation organisms, was invented in the year 1590, but Leeuwenhoek, in Holland (1632-1723), was the first to
? The bracketed numbers given in this section relate to the bibliography at the end of the book. To the latter we have appended explanatory notes bringing in many amplifications and explanations which could not find a place in this short introduction.
employ it in making a close study of these forms of life. He was followed by a number of distinguished microscopists who all, more or less, added to our knowledge of the natural history of micro-organisms. All these were descriptive and systematic morphologists and not experimenters. Of the more distinguished microscopists who followed Leeuwenhoek we may mention the names of Otto Friedrich Müller (1730-85), in Denmark, and Ehrenberg (1795-1876), in Germany.
In the year 1822 Persoon gave to yeast the systematic name Mycoderma, a designation which seems to indicate that he regarded it as a fungus (mycoderma signifies fungoid film).
About the same time—in the middle of the thirties Cagniard Latour (V. 1, 2), Schwann (VI. 1, 2) and Kützing (VII.) stated expressly that yeast is a plant. Meyen agreed with this view and gave to the new genus the systematic name of Saccharomyces (i.e., sugar fungus) which it has since retained.
Considering the state of knowledge at that time, very valuable contributions to the natural history of yeast fungus were made by Eilhard Mitscherlich. It is evident from a paper published by him in 1841 (IX. 1), that this investigator recognised the substance invertin. In 1843 (IX. 2) he read a paper on the multiplication of yeast; he had observed under the microscope the phenomenon of budding, and had followed the development from a single cell.
Schwann, Cagniard Latour and Kützing expressed the opinion that it is the living yeast cell which excites alcoholic fermentation. In direct opposition to this vitalistic theory, Justus v. Liebig (1839-40) came forward with his theory of mechanical decomposition (VIII. 1). According to Liebig, every fermentation consists of molecular motion which is transmitted from a substance in a state of chemical motion, that is, of decomposition, to other substances the elements of which are loosely bound together. In his last work on fermentation (VIII. 2), he sought to bring this theory into agreement with the observations of Louis Pasteur on auto-fermentation. Liebig's explanation of the latter is that the cells contain a decomposing substance which produces sugar for the auto-fermentation. Although he at first looked upon yeast as a lifeless mass, an albuminoid compound, yet he came gradually to the view that it consists of living cells. But, in his opinion, there could be no question of fermentation being a physiological process: in this respect he held to his chemical conception.
At that time a vigorous dispute was taking place between the followers and the opponents of the doctrine of generatio æquivoca, i.e., of spontaneous generation. Let us look somewhat closer at this doctrine. By spontaneous generation we understand the development of organisms from lifeless material without eggs, seeds or embryos. Needham (1745), an energetic supporter of this doctrine, was the first to make experiments endeavouring to prove it. For this purpose he heated meat extract in closed flasks, and, on organisms appearing in the flasks, he assumed that they had been produced by spontaneous generation.
Spallanzani (1765) showed, however (I.), that certain errors were made in these experiments; he sealed his flasks hermetically and boiled them for an hour, after which treatment no development of micro-organisms could be observed. From his experiments he concluded that the "eggs” of the micro-organisms are present in the air and only develop after they have found their way into the liquid.
On these experiments the foundation of the technique