1. The loss of weight in pigeons subjected to prolonged starvation on water alone may be accurately represented by an appropriate form of the law of autocatakinesis. 2. This function, within proper limitations, gives a definite indication as to the nature and character of the fundamental reactions involved. In addition, it provides quantitative measures of the relative progress and importance of these reactions. 3. Analytically, the process of starvation consists of two nearly symmetrical cycles, corresponding chemically to the destruction of the carbohydrate-fat reserves and to the decomposition of body protein. 4. A suitable transformation overcoming certain difficulties inherent in the general form of the law is discussed and applied to the data reported.