Authors who have written on the subject of wine attributed this malady to the rising of the lees. They believed that the deposit which always exists in greater or less quantities in the lower part of the cask rises and spreads itself into all the mass of the wine. Nothing can be more inexact. If this phenomenon is sometimes produced--that is to say, if the deposit rises into the mass of wine--the effect is due to a sudden diminution of the atmospheric pressure, as in times of storm, for example. As the wine is always charged with carbonic acid gas, which it holds in solution from the moment of fermentation, one can conceive that a lowering of barometric pressure would cause the escape of some bubbles of carbonic acid. These bubbles, rising from the lower part of the cask, may disturb a portion of the deposit, which then mixes with the wine and renders it turbid. But the real cause of the disease is quite different. The turbidity is without exception due to the presence of little filaments of an extreme tenuity, about a thousandth part of a millimeter in diameter. Their length is very variable. It is these which, when the wine is agitated, give rise to the silky waves just referred to. Often the deposit of the casks leaves a swarm of these filaments entangled in each other, forming a glutinous mass, which under the microscope is seen to be composed entirely of these little filaments. In acting upon certain constituents of the wine particularly upon the tartar, this ferment generates carbonic acid. The phenomenon of spurting is then produced, because when the cask is closed the internal pressure of the liquid augments. The sparkling and the crown of little gas-bubbles, observed when the turned wine is poured out into a glass, is similarly explained. In a word, the disease of turned wine is nothing else than a fermentation, due to an organised ferment which, without any doubt, proceeds originally from germs existing on the surface of the grapes at the moment of gathering them, or on spoilt grapes such as are found in every vintage. It is very rare not to find this parasite of turned wine in the deposit of the wine at the bottom of the casks, but the parasite is not troublesome unless it multiplies very largely. Pasteur found the means of preventing this multiplication by a very simple remedy, equally applicable to other diseases of wines, such as that of bitterness or greasiness (_maladie de la graisse_).