Another cause of the deterioration of the quality of vinegar, which is sometimes very annoying to the manufacturer, consists in the frequent presence of little eel-like organisms, very curious when viewed with a strong magnifier. Their bodies are so transparent that their internal organs can be easily distinguished. These eel-like creatures multiply with extraordinary rapidity. Certainly there is not a single barrel of vinegar manufactured by the Orleans system which does not contain them in alarming numbers. Prior to Pasteur's investigations, the ignorance regarding these organisms was such that they were actually considered necessary to the production of the vinegar; whereas they are, on the contrary, most inimical to it, and must, if possible, be got rid of. This is, moreover, rendered desirable by the repugnance which is naturally felt to using a liquid defiled by the presence of such animalcules--a repugnance which becomes almost insurmountable to anyone who has once seen through a microscope the swarms contained in a drop of vinegar. The mischief wrought by these little beings in the manufacture of vinegar results from the fact that they require air to live. The effect can easily be perceived by filling to the brim a bottle of vinegar, corking it, and then comparing it with a similar bottle half filled with the same vinegar, and left uncorked in contact with the air. In the first bottle, the motions of the eel-like creatures become gradually slower, until after a few days they cease to multiply and fall lifeless to the bottom of the vessel. In the second bottle, on the contrary, they continue to swarm and move about. This need of oxygen is further demonstrated by the fact that, if the vinegar reaches a certain depth in the bottle, life is suspended in the lower parts, and the little eel-like organisms, in order to breathe more freely, form a crawling zone in the upper layers of the liquid.