*BACILLUS TUBERCULOSIS _to face_ 280 *BACILLUS TUBERCULOSIS " 280 *STREPTOCOCCUS PYOGENES " 280 *BACILLUS ANTHRACIS " 280 FLASK USED IN THE PREPARATION OF TUBERCULIN 282 BACILLUS OF DIPHTHERIA 289 TYPES OF STREPTOCOCCUS 298 MICROCOCCUS TETRAGONUS 299 DIPLOCOCCUS OF NEISSER 300 BACILLUS OF ANTHRAX AND BLOOD CORPUSCLES 302 THREADS OF BACILLUS ANTHRACIS, SHOWING SPORES 302 BACILLUS OF PLAGUE 306 *BACILLUS OF PLAGUE _to face_ 310 *BACILLUS OF LEPROSY " 310 STREPTOTHRIX ACTINOMYCES " 310 BACILLUS MALLEI " 310 DIPLOCOCCUS OF PNEUMONIA 312 BACILLUS OF INFLUENZA 315 INTRODUCTION We live in a world that is teeming with life. From the earliest times of man that life has been studied and the observations recorded. Thus there has slowly come to be a considerable accumulation of knowledge concerning the various forms (morphology) and functions (physiology) of organised life. This we call the science of biology. It has for its object the study of organic beings, and for its end the knowledge of the laws of their organisation and activity. Slowly, too, in the midst of this gradual accumulation of facts, we begin to see incoherence becoming coherent, chaos becoming cosmos, chance and accident becoming law. Further, the contemplation and comprehension which built up the edifice of modern biology is assuming a new relationship to practical life. Biology can no longer be considered only as an academic occupation or as a theoretical pabulum upon which the leisured mind may ruminate. With rapid strides and determined face this giant of knowledge has marched into the arena of practical politics. The world is opening its eyes to a reality which it had mistaken for a vision.