The resemblance between these filaments and those which, in considerably smaller proportion, accompanied the globules of alcoholic ferment in our preceding observations, the change in the beer, which was almost as bad as beer could possibly be, along with an abundance of filaments, and the change, to a minor extent, in that beer which only presented a few filaments in a field of the microscope, impressed those managers of the brewery who were present with an entire belief in the theory which we had been endeavouring to impress on their minds concerning the causes of the badness of their beer. Some eight days afterwards we paid another visit to this same brewery, and learnt that the directors had lost no time in acquiring a microscope, and in procuring changes of yeast for all the varieties of beer, which they had put in working since our first visit. There are some periods of the year—early spring, summer, and autumn, for instance—when the working of a brewery is a matter of great difficulty. The preservation of yeast becomes a subject requiring the most delicate treatment, in consequence of the increase in the temperature. In the early part of autumn the most important ingredients used in brewing are of inferior quality; the deteriorating influences which have been at work have covered them with a variety of parasites. All these circumstances contribute to facilitate the development of diseased ferments. § II.—The Absence of Change in Wort and Beer Coincides with the Absence of Foreign Organisms. The method which we have just pursued in demonstrating the existence of a relation between the diseases of beer and certain microscopic organisms can scarcely leave a doubt, it seems to us, as to the correctness of the principles which we are advocating. In every case where the microscope reveals in a yeast, especially a yeast which is in a state of activity, products which are foreign to the composition of alcoholic ferment, properly so called, the flavour of the beer is more or less unsatisfactory, according to the abundance or nature of these minute organisms. Moreover, when a finished beer of superior quality loses in the course of time its agreeable flavour, and becomes sour, it may readily be shown that the alcoholic ferment in the deposit existing in bottles or casks, although originally pure, at least in appearance, becomes gradually intermixed with these same filiform ferments or other ones. These facts may be deduced from what precedes; nevertheless, some prejudiced minds might perhaps urge that these foreign ferments are the consequence of some diseased condition, produced by circumstances of which we know nothing. Although this gratuitous supposition may be difficult to sustain, we shall endeavour to corroborate our preceding observations by the method of experiment which will be seen to be the more decisive.