Emil Chr. Hansen 5 Særtryk 1901-1909

588 HANSEN : CONSIDERATION’S ON TECHNICAL MYCOLOGY. organisms on many of our manufacturing processes and with the manner in which they make their influence felt in practical life, both in beneficent and in injurious ways. The diseases caused by these organisms in animals and in plants are excepted—the study of these belongs to pathology. The most important organisms with which the technical mycology has to deal are those minute beings which can only be observed with the aid of the microscope, associated with so-called fermentative changes. The chief aim of technical mycology is, as we know, to attain practical results, and I purpose restricting myself to those domains of the exceedingly extensive field covered by this branch of science in which practical results have been achieved. Microscopical organisms were used, even on a large scale, long before people had the faintest idea of their existence—for instance, in the making of beer and wine. Leeuwenhoek, the Dutch microscopist, was the first who saw yeast-cells and bacteria. In some of his famous letters, which in 1680 and the following years he sent to the Royal Society of London, he gave a description of these organisms, accom- panied by figures. Very many years passed by, however, before it was conclusively demonstrated that these organisms were the originators of fermentation. The proof of this as regards alcoholic fermentation is contained in a series of papers published in the years 1836—1839 by Cagniard Latour, Schwann, and Kiitzing; the last-mentioned observer also showed that the formation of acetic acid was due to the presence of bacteria. The doctrine that fermentation is caused by micro- organisms was attacked by Liebig, and it was not till Pasteur’s time that it became firmly established. It was, in fact, by Pasteur’s researches that practical zymotechnologists were first brought to see that the manufacture of wine, beer, and vinegar is, to a large degree, a function of the life-history of certain micro-organisms. These researches further demonstrated to them the important fact that some bacteria are responsible for diseases in wine and beer. This period in Pasteur’s researches synchronises also with his studies on spontaneous generation, by which expression is understood the development of living organisms from dead matter, especially from amorphous organic matter, without eggs, seeds, or germs. There have been naturalists at all epochs who embraced this view, which was revived by the writings of Needham in the years 1745—1756. One of Needham’s experiments consisted in strongly heating meat