The Outline of Science was written specifically with the man-on-the-street in mind as the target audience. Covering scientific subjects ranging from astronomy to biology to elementary physics in clear, concise and easily understood prose, this popular science work is largely as relevant today as when first published in 1922. In this fourth volume (of four), we learn about bacteria, luminous organisms and lower vertebrates as well as domesticated animals. Other chapters are devoted to ethnology, health, relativity theory and philosophy of science. (Summary adapted from the first three volumes by Availle.)