For thousands of years animal substances of various degrees of nastiness have been used as medicines. In fact some of the darkest chapters of human history are those relating to this subject. Sundry cognate superstitions are extant to this day, even among the nobility of civilized countries. In ancient times weird ceremony and occultism lent their charms to keep up interest in the matter; while in these “scientific times” the influence of a great hyphenated name has rekindled a fire which was merely flickering and which seemed to be in danger of going out altogether. Since Brown-Sequard made himself young again by his well known treatment of senility great attention has been paid to the subject of animal extracts. From every corner of the earth have come workmen—some of them skilled workmen—to cultivate this promising field. One result of their labor is a mass of literature which contains much that is premature, much that is fantastic, much that is commercial; and it is difficult not to believe that some of it is closely connected with unsoundness of mind. Another result is the new method of treating myxedema by the administration of thyroid glands—raw, cooked, desiccated, or in the form of extracts. Recently this treatment has been used in several cases with marked success, and already the air is full of rumors. One writer said a few months ago: “The success of this treatment is sure to create a ‘_boom_’ in animal extracts for various diseases.” He proved to be a true prophet, and we are in the midst of this _boom_. It may perhaps be open to question whether there was need of any more “booms.” We have had “booms” in tuberculin, in coal-tar, in ovariotomy, if not in common sense. Some of them are still with us, though not in very good condition. After the boomers and the seekers after notoriety have done their worst with animal extracts, the final accounting will probably show some increase of positive knowledge in physiology as well as in therapeutics. BACTERIOLOGY. Bacteriology having now emerged from noisy babyhood into promising youth, it may not be amiss to ask how far therapeutics has been advanced by its discoveries and what the outlook is for the future. It has been alleged by some clinicians that the bacteriologists have been a little dictatorial, and have carried on their propaganda somewhat after the manner of the Salvation army. Be that as it may, the amount of conscientious and unremunerated work which has been devoted to the subject during the past twelve years is probably beyond the power of conception of any one man.