"Of the natural ferments two have been resorted to. One is mentioned by Grieve, which he borrowed from the Bashkirs of Orenbourg, and which simply consists in the addition of one sixth part of water and one eighth of the sourest cows' milk to fresh mares' milk; the other has been employed, and was, if I mistake not, first recommended by Bogoyavlensky. It is a very simple if rather a tedious method. New mares' milk, diluted with one third its bulk of water, is placed in the _saba_,[21] and while allowed to sour spontaneously, is continually beaten up. This milk gradually undergoes the vinous fermentation, and in twenty-four hours is converted into weak koumiss. The disadvantage of this mode of commencing fermentation is obvious—viz., the great waste of time in agitation. Hence it is only employed when no artificial ferment is obtainable. "In starting the process of fermentation in mares' or any other kind of milk, therefore, an artificial ferment is more frequently employed than a natural one. The former is used only for converting the first portion of milk into koumiss; the latter is always resorted to afterwards. "Of artificial ferments the variety is great, for besides all putrefying animal matters which contain nitrogen—such as blood, white of egg, glue, and flesh—certain mineral substances which act by souring the milk are also capable of exciting fermentation. "Now, many of the nomads, whose mares either give no milk or are not milked in winter, commence the preparation of their koumiss in spring by borrowing a ferment from the animal, mineral, or vegetable kingdom. Thus a mixture of honey and flour is the favourite ferment with some races of nomads; a piece of fresh horse-skin or tendon is preferred by others, while a few resort to old copper coins, covered with verdigris, for starting fermentation. In the choice of a ferment they are guided solely by habit and tradition. As it would be useless, almost impossible, to give a list of all the foreign substances that have been employed with the view of converting mares' milk into koumiss, it will be best to consider the simplest artificial ferments, and those most generally in use.