THE DAIRY. 277 



of its cream, is kept for a time, the caseous matter diffused 

 through it, or dissolved in it, coagulates and forms curd. 

 This coagulum envelopes the parts which still remain liquid, 

 and renders the whole of a gelatinous consistence. By 

 pressure, and breaking the coagulum, the greater part of the 

 liquid readily separates, and the curd, being compressed, 

 forms cheese. But the process of coagulation may be has- 

 tened by the mixture of various substances. All the acids 

 possess the property of coagulating milk, even at common 

 temperatures, and more readily when assisted by heat. Even 

 alcohol, gum, sugar, and soluble neutral salts, produce the 

 formation of curd. Certain vegetable principles, as tannin, 

 and the juices of numerous plants, likewise coagulate milk, 

 as an infusion of the stems or leaves of sorrel, of butterwort, 

 of ladies' bedstraw, of the flowers of the artichoke, and of 

 the roots of the marsh-marigold. But the substance the 

 most approved of for producing coagulation is runnet, whic 

 is prepared by macerating the stomach of a sucking animal 

 in water, so as to extract the gastric juice, of which a very 

 minute quantity, contained in the infusion, suffices to coagu- 

 late a large quantity of milk. As acids promote the coagu- 

 lation of milk, so the alkalies prevent it, by rendering the 

 caseous matter soluble. When, therefore, soda, potassa, or 

 ammonia, exists in milk, coagulation will not take place 

 until the alkalies are neutralized by the addition of acids, or 

 by their spontaneous formation in the milk. 



After the curd has been formed, either by the slow forma- 

 tion of acids in the milk, or by the addition of coagulating 

 media, the curd is broken, and the liquid which it envelopes 

 is separated by pressure. The expressed liquid is Whey ; 

 and whey, therefore, is merely milk deprived of its cheesy 

 matter. Whey accordingly contains butter, in so far as the 

 cream has not been separated, and butter, therefore, may be 

 derived from whey. It contains likewise the sugar of milk, 

 which may be obtained separately, in the crystalline form, 

 by evaporation ; and, in certain parts of Europe, the sugar 



