Nothing is more susceptible to external influences, as has been remarked elsewhere, than milk and cream, both of which are liable to taint from the food of the cows, from impurities derived from careless milking, from exposure to foul or impure air in the cellar or milk-room, and from sudden changes in the atmosphere. The most scrupulous cleanliness is, therefore, required to produce a first quality of cheese, even under favorable circumstances. And when it is considered that it is necessary to observe minutely the temperature of the milk, and that slight differences at the time of forming the curd may make the difference of mellowness or toughness in the ripened cheese, and that the proper temperature is affected by the time taken to bring the curd, which depends on the strength and quality of the rennet, some of which will act in fifteen or twenty minutes, while the same quantity of others requires even two or three hours to produce the same effect, the infinite variety in the qualities of cheese will scarcely be a matter of surprise. A brief statement of the mode of making some of the more important and well-known varieties will be sufficient in this connection. The details of cheese-making in some of the best of the dairies of New England and New York correspond in a remarkable degree with the mode of making Cheddar and Cheshire cheese, both celebrated for their richness and popularity in the market. Of the latter there are made, it is said, over twelve thousand tons annually; Cheshire taking the lead in cheese-making, and keeping about forty thousand cows.