For this reason the rennet which is to be used should always be tested in small quantities of milk beforehand in order that the proper proportion to be used may be known so that the process in a large way may be conducted with certainty and not by guess. (“British Dairy Farming,” by Jas. Long.) Rennet is sometimes treated with borax to preserve it during transit. In such cases the borax may not all be removed by the whey and is consequently found in ripened cheese. Its introduction in this way should be avoided. _Coagulating the Milk by Rennet Extract._--This process is often termed by the cheese makers “setting the milk with rennet.” The milk which is used for the purpose of cheese making should be, in the technical language of the cheese maker, “ripe,” that is, containing a sufficient quantity of lactic acid. The principal method of producing the proper amount of lactic acid in milk is by keeping it warm, namely, at a temperature of about 84 degrees. At this temperature the most favorable conditions exist in milk for the rapid growth of the lactic acid ferments. If the natural ferments which produce lactic acid are not in sufficient quantity in the original milk it is better, rather than to wait too long a time, to start the development of the lactic acid by adding an artificial ferment. Lactic ferments are specially prepared for this purpose, or some previously ripened milk may be added to the mass. This is called a “starter.” From two to five pounds of “starter” are usually required for each one hundred pounds of milk. The degree of ripening is ascertained by measuring the quantity of lactic acid present. The proper condition of the milk is tested by means of a rennet preparation and if the milk will coagulate, when thus tested, in about one minute or a little more it is an indication that a sufficient amount of acid has been developed to add the rennet for the proper coagulation of the milk. It is important to have the milk in just the right condition in order that the proper operations in cheese making may go on uniformly. Care must be taken, however, not to have too much lactic acid in the milk. For instance, 0.2 of one percent is too great, and such a milk is very liable to give trouble in subsequent operations. In the curding of milk by rennet the temperature should be kept between 82 and 86 degrees. The amount of rennet extract, of course, varies with its character and strength, and this is best determined by the cheese maker’s experimenting in order that the proper quantity to be added to the great mass of milk may be known beforehand. A sufficient quantity of rennet extract should be used to curdle the milk in fifteen or twenty minutes for a quick-curing cheese, and in thirty to forty minutes for a slow-curing cheese. The rennet extracts in common use are added at the rate of from one-half to five ounces for 1000 pounds of milk. Before adding, the extract should be diluted