The main interest in the metabolism of the lens has been centered around the quantitative analysis of protein, cystine, glutathione, cevitamic acid, tyrosine, calcium and cholesterol. A host of other substances have been disregarded in spite of the obvious great complexity of these substances and their reactions. If an analysis of a clock enclosed within a case of pressed casein is made, little is revealed concerning its nature except that it is composed of protein, carbohydrate, lipid, phosphates, calcium, iron, copper, zinc and water. Important as it may be, a similar analytic description of a lens is the chemical picture of a dead lens, but a living lens is the result of many complex dynamic processes which are simultaneously and constantly occurring to give it life and growth. The sum of the physical and chemical processes by which the living lens is produced and maintained is called its metabolism.