of putrefactive processes, must be ascribed to the same or to similar causes. § 2. The refutation of this view by Liebig seems satisfactory, and has not yet been satisfactorily replied to. The subject is one of much interest; the theory has furnished a foundation for some unquestionably entirely fallacious ideas concerning the essence of the vital processes generally, of many pathological conditions, and the causes of certain diseases. These persons regard fermentation, or the resolution of higher or more complex organic vegetable atoms into less complex compounds, as the effect of the vital manifestations of vegetable matters; and putrefaction, or the same change in animal substances, as being determined by the development or the presence of animal beings. They assume as a natural consequence of this view, that the origin of miasmatic or contagious diseases, in so far as referrible to the presence of putrefactive processes, must be ascribed to the same or similar causes. The most obvious and important considerations in support of this view of fermentation, are derived from observations made on the alcoholic fermentation, and on the yeast of beer and of wine. The microscopic researches of physiologists and botanists have demonstrated that beer or wine yeast consists of single globules strung together, which possess all the properties of living vegetable cells, and resemble very closely certain of the lower family of plants, such as some fungi and algæ. In fermenting vegetable juices, we observe, after a few days, small points, which grow from within outwards; and these have a granular nucleus, surrounded by a transparent envelope. The simultaneous appearance of the yeast-cells and of the products of decomposition of the sugar, is the chief argument in support of the opinion that the fermentation of sugar is an effect caused by the vital process, a result of the development, growth, and propagation of these low vegetable structures. But if the development increase, and propagation of these vegetable cells or tissues be the cause of fermentation, then in every case where we observe this effect we must suppose that the causes or conditions--namely, sugar, from which the cell-walls are produced, and gluten, which yields their contents--are both present.