Emil Chr. Hansen 5 Særtryk 1901-1909

HANSEN: CONSIDERATIONS ON TECHNICAL MYCOLOGY. 591 hint to me, indicating as it did to my mind, that the most important secrets were hidden in the yeast itself. In my experiments I started from the idea that these cells, which looked so very much alike under the microscope, must, notwithstanding, belong to different species and races. In order to gain progress in this new field it was necessary for me first to work out an exact method of pure cultivation starting from one single cell. The next step was to resolve brewing-yeast into its components. The result showed that other yeasts, disease-yeasts, were found together with the beer-yeast proper, and that, what was commonly called the beer-yeast proper, the Saccharomyces Cerevisiæ, was not a biological entity, but could be resolved into different species and races, each of which had the power of imparting to beer a definite character. Thus I was step by step led to introduce into the bottom- fermentation breweries a yeast consisting of a pure culture of one single selected species or race. This was done in 1883. These practical researches thus inaugurated an experimental study of yeasts, the word being used in its broadest sense. Each of the supposed species was found to consist of several species and laces. With regard to the acetic acid bacteria, I had some years previously shown that what was till then known as the “ vinegar plant,” Myco- derma aceti, consisted of at least two species. This resolution of sup- posed species has since then been gradually carried further and further, and has led up to investigations which have given a new insight into the lives and activities of these organisms, and a new conception of the term “ species,” from which, later on, studies on variation and heredity were started. This movement was, as I emphasised, chiefly set on foot by the problems which cropped up in the industries where these organisms were used. Practical and theoretical problems go hand in hand in this field. I have given a description of ■ these different researches in my “ Practical Studies in Fermentation,” of which a second edition is now in preparation. When we survey the manner in which the advances have been made, it becomes clear that they are due more to the force of existing circum- stances than to any single investigator. This holds good with regard to my own work. The time was specially favourable to their appear- ance : our science had reached a point where the next link must come. The Carlsberg Laboratory had just been founded, and by this I got the most excellent apparatus at my disposal. Stress must furthermore be b 2