A Computer Analysis Method For Thermal Diffusion in Biochemical Systems In the thermal detection of rapid biochemical reactions it is necessary to correct the temperature data for transient heat conduction losses in a cylindrical calorimeter. To handle the complexities arising from varying thermal-relaxation times of concentric insulating layers, a computer program was developed which gives the temperature distribution of the system as a function of radius and time. This distribution is corrected at each step by a subroutine which calculates the instantaneous chemical state of there action, as well as the heat produced by this reaction. The program is based on a direct statement of Fourier's law of heat conduction and the chemical rate equation to provide a "bookkeeping law" to follow the reactants and the flow of heat packets, in such a way that the computer continually stores the heat distribution. A computer analysis method is here regarded as one in which the physical laws of a process are used explicitly in the program. Usually this results in by passing much of the mathematical procedures conventionally used. The program was tested against some known exact solutions of the heat equation and gave identical results, and compared well with experimental data of a known biochemical reaction. The construction of computer programs based on the direct statement of the physical laws is a principle of general applicability which has been applied to several other physical phenomena. CACM September, 1964 Davids, N. Berger, R. L. CA640908 JB March 9, 1978 5:13 PM 1003 5 1003 1003 5 1003 1003 5 1003