In raw milk the fat globules are largely found in larger or smaller aggregates, rather than uniformly distributed throughout the serum. The surface of a mass of fat globules is smaller in proportion to the volume of the mass than is the case with single globules, hence globule clusters encounter less resistance in their passage through the serum, either as they rise to the surface in gravity creaming, or in the separator bowl. If these clusters are broken up, so that the globules are uniformly distributed, the milk will cream much less rapidly and completely. In the process known as "homogenization" of milk, the individual fat globules are broken into such small globules, that they cannot overcome the viscosity of the serum, and they remain distributed throughout the milk. In such cases, no cream rises, and even the cream separator is unable to remove the fat from such milk. In selling bottled milk, it is highly desirable that the cream line should show distinctly. In normal milk, this line forms in a few hours, but where milk is heated to a high temperature, and agitated at the same time, the clusters of fat globules are broken apart and the creaming power injured. This physical change is dependent not only on the temperature, but also on the time of exposure. A momentary exposure at 160° F., or for 20 minutes at 145° F., is about the maximum limit which can be applied to milk without material injury to the creaming property. [Illustration: Fig. 25.--Fat Globules in Raw Milk. In raw milk the fat globules are in masses of varying sizes. These rise to the surface quickly in gravity creaming.] The body or consistency of pasteurized cream may be restored by allowing the cream to stand for several days at low temperatures, or by the addition of a small amount of sucrate of lime. This substance, known to the dairy trade as "viscogen," is made by adding to a thick solution of cane sugar, some freshly slaked lime. The sugar solution permits of the dissolving of a much larger amount of the lime than is possible in water. When the liquid is allowed to settle, the clear solution is then decanted off and is used at the rate of about one part to 100 to 150 parts of cream. The fat globules are, by its action, brought into aggregates and the body of the cream thus restored. Viscogen contains nothing that is at all harmful, but milk and cream to which it is added must be sold under some distinctive name as "visco-cream," since the laws of practically all states do not allow the addition of any substance whatever to milk or cream. [Illustration: Fig. 26.--Fat Globules in Heated Milk. When milk is heated the masses of globules are broken up and fat globules are uniformly distributed throughout the milk.] [Illustration: Fig. 27.--Creaming of Milk.