With starch it is an entirely different matter. It has been found that the application of heat, either as dry heat, or in the presence of moisture, brings about a definite change in the character of the foodstuff. Pure starch admixed with water and boiled, passes into a condition of colloidal dispersion, or semi-solution, known as starch paste (Sherman). This is graphically illustrated in the cooking of potatoes, in which the starch and water are mixed in nature; and in the cooking of cereals and like starchy foods, to which water is added in preparation for their cooking. In both cases the application of heat adds greatly to the digestibility of the raw material by reason of the change which is wrought in these substances, causing them to be more readily acted upon by enzymes in the digestive juices. This solubility of carbohydrates in hot water may be utilized in the washing of utensils in which these substances have been prepared; thus saving much time and effort on the part of the nurse in either the diet kitchen or in the home. FATS The second member of the organic food group, and one which is almost as widely distributed throughout animal and vegetable life as the carbohydrates, is found in the fats. This foodstuff, while composed of the same chemical elements that go to make up the carbohydrates, contains these elements in different proportions; that is, fats contain less oxygen and more hydrogen than carbohydrates. ~Typical Fats.~--The fats (as already shown in the Table on page 5) are derived from both animal and plant life, but, like the carbohydrates, do not always occur in the same form. Those of animal origin include: ~Adipose Tissue~ of man and animals, tallow of mutton, suet, and oleo oil of beef, lard of pork. ~Phosphorized Fats~, which include lecithin and lecithans, occur abundantly in the brain and nerve tissues and to a less extent in the cells and tissues of man, animals, and plants of which it seems an essential part. Egg yolk is the most abundant source of phosphorized fat in food material, but milk likewise furnishes an appreciable amount. ~Cholesterol~ (fat-like substances).--"The fatty secretions of the sebaceous glands of man and of the higher animals which furnish the natural oil for hair, wool and feathers," (Starling), lanoline, which is a purified wool fat, consist chiefly of cholesterol. According to Mathews, cholesterol is an essential constituent of the blood, and is found in the brain and in nearly all living tissues. It is likewise believed to be the "mother substance" from which bile acids are derived. ~Fat Soluble "A."~--The vitamine factor which occurs dissolved in certain fats, namely, milk (whole), butter, egg yolk, the organs of animals, and codfish liver.