Consequences are derived from the following assumptions about the birth rate of stars in the entire Galaxy: (1) this rate is proportional to a time-independent function `p of magnitude AL (2) `p is given by the luminosity function for young galactic clusters; (3) the birth rate per some volume is proportional to the gas mass in this volume. It is found that an appreciable fraction of the galactic mass was converted into stars in less than a billion years and that the mass of gas at present decreases only very slowly with time. Predicted luminosity functions are derived, and comparison with observation shows that the stellar birth rate should increase slightly more strongly with gas density than in assumption 3. It is found that white dwarfs constitute about 0.17 of the total present number of stars. The total luminosity of the Galaxy is derived as a function of time. From a simple model for stellar helium production, the helium abundance in the gas is derived as a function of time. At present, this abundance for the gas is about four times the average abundance for gas plus all stars. Assuming medium-heavy nuclei to be produced by supernovae breakup of massive stars, their abundance in the gas is derived as a function of time.