IN the Preface to Plant Biology we discussed the general point of view that we believed should be emphasized in a course in elementary biology for students of high school age. We there stated that in our judgment the primary emphasis in the whole course should be placed on the many relations of biology to human welfare. Many. Of the experiments in that volume, especially those relating to the chemical com position of lifeless and living things, the tests for the food substances, and the principles of osmosis and of respiration, apply equally well in the discussion of animal and human biology.