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.

"The simplest way is that recommended by Bogoyavlensky, and adopted and modified by Tchembulatof.22 It is prepared thus: 'Take a quarter of a pound of millet-flour, add water to it, and boil it down to the consistence of thick oatmeal porridge. Then heat separately, in another vessel, eleven pints of milk to boiling-point, and allow it to cool down. When its temperature has fallen to 95° F., pour it into a wooden bowl or tub, and add the boiled flour to it. The upper and open part of the vessel is then covered with a piece of coarse linen, and left at rest—at a temperature of about 99° F.—from twenty-four to forty-eight hours. The appearance of small bubbles, which keep bursting on the surface of this liquid, combined with a vinous or acid odour, prove that the ferment is ready. To this fermenting fluid twenty-two quarts of new milk are gradually (i.e., every ten minutes) added, and the whole mass is continuously beaten up for twelve hours. The temperature during stirring should never be higher than 94° F. The whole fluid soon begins to ferment, and after twelve hours a not unpleasant koumiss is ready. This should be filtered through a horse-hair or muslin sieve, after which it is fit for drinking. This liquid is called weak koumiss; but a limited portion of the lactine has undergone the lactuous and vinous fermentations, and thus the percentage of alcohol is small. Koumiss at an ordinary temperature remains weak for twelve hours after it has been beaten up, and then gradually passes into medium.'"

Curiously enough, the richness of cows' milk in fat militates against its being a good raw material for the making of koumiss, owing to the production of small quantities of butyric acid, which follows upon the fermentation, so that it is desirable, if koumiss is to be prepared from cows' milk, that the fat should be first of all eliminated, so that the separated milk will then approximate to the composition of mares' milk.

"The chemical changes," says Hutchison,23 "which take place in the milk under the double fermentation are not difficult to follow; the lactic ferment simply changes part of the sugar into lactic acid, the vinous ferment eats up a very small part of the proteid of the milk, and, at the same time, produces from the sugar a little alcohol and a good deal of carbon dioxide; the milk thus becomes sour, it effervesces and is weakly alcoholic, but the lactic acid causes the casein to be precipitated just as it does in the ordinary souring of milk, and the casein falls down in flocculi."

As will have been noticed, it is an essential part of the process of koumiss-making to keep the milk in a state of agitation during the period of fermentation, a process which is intended to permit of oxygen being taken up by the fermenting fluid, while, at the same time, the casein is broken up into a state of fine division. The casein also, or at least a portion of it, becomes very soluble, and after twelve hours of fermentation the taste of the product is only slightly sour, and the milk taste still remains. This taste, however, disappears in twenty-four hours, owing to the rapid development of the lactic acid organisms. After this lapse of time the sugar is entirely destroyed, and the strong koumiss which results is a thin sour fluid which effervesces briskly, and in this condition will keep for an indefinite period. "The net change which has taken place in the original milk may be summed up by saying that the sugar of the milk has been replaced by lactic acid, alcohol, and carbon dioxide, the casein has been partly precipitated in a state of very fine division, and partly pre-digested and dissolved, while the fat and salts have been left much as they were."24

Violent stirring or agitation of the cultures does not seem to work so much by supplying oxygen to the fermenting liquid, as by ensuring a thorough distribution of the micro-organisms throughout the liquid, and thus dividing the casein.

The greater number of the organisms are facultative anærobes and oxygen is not necessary. Again, koumiss put up in bottles on the first day is regularly shaken although air is excluded.

Keffir.—Keffir is a kind of fermented milk which has been in use in the Caucasus for quite a long time, as koumiss has been in the steppes. It differs from koumiss, however, in this respect, that it is prepared from either sheep's, goats', or cows' milk. The process is started by the addition of keffir grains to the milk, which is contained in leathern bottles. These keffir grains are small solid kernels which are kept in families and handed on from one generation to another.25 The grains are the origin of the ferment, as they disseminate in the milk