Emil Chr. Hansen 5 Særtryk 1901-1909

HANSEN : CONSIDERATIONS ON TECHNICAL MYCOLOGY. 593 Saccharomyces is used, and at its conclusion a torula is added, in both cases pure cultures. It holds good with regard to the different beer yeasts that they can give different products, and the same is also the case with the Torulæ. It is probable that each of the English and Scotch types of beer will demand not only its own saccharomyces, but also its own torula. If these types are still to be kept up, due attention must be paid to this. I have treated of this subject at some length because of its special interest to the brewers over here. Many of the fermentations used by us are of a compound nature; this is the case in the manufacture of butter and cheese. By Storch’s researches in 1890 it was proved that the souring of cream was caused by certain bacteria, some of which produce a specially fine flavour. By this the impulse was given, also in that domain, to try the employ- ment of pure cultures. In most of the cases these cultures consisted of several species of bacteria • sometimes also of yeasts and Oidia. They have been placed on the market and are prepared in different institutes, each of which keeps its own method secret, so that the practical worker does not know what he buys. Public control is wanting, and it has proved a source of detriment to the safe develop- ment of this matter that it is enveloped in secrecy. Several scientists have also during late years been actively engaged on experiments, the object of which is the employment of pure cultures for the ripening of some of the finer sorts of cheese. In some instances mould-fungi are especially used, in others bacteria. These labours will certainly, in the immediate future, lead to results of great practical importance. Technical mycology has gradually extended its domain so as to embrace many other manufactures besides those I have spoken of above. I shall only mention here the manufacture of vinegar and conserves, breadmaking, the sugar, tobacco, and tanning industries. In recent years a new branch of bacteriology has been established : it deals with the activity of bacteria in the soil, and especially with the relation between them and the higher plants. This branch is also considered as being within the pale of technical mycology. In 1886 Hellriegel and Wilfarth made the important discovery that some of the bacteria in the soil could enter into a symbiosis with certain culti- vated Leguminosæ, enabling these to assimilate the free nitrogen contained in the air. By this it is possible to increase the production