The tubercle bacillus can form resting spores; consequently, when once the tissues of a part have their vitality so lowered that the entrance of the bacilli is allowed, they can retain their hold with great tenacity. Although the bacilli can not develop outside the body, their vitality is preserved for a long time. Certain animal products used for food, such as the milk of tubercular cows, contain the bacilli. Experiments such as causing animals to inhale the tubercle bacilli, or the introduction of them into the blood, or sometimes the feeding on tubercular matter, result in tuberculosis. Pulmonary consumption presents an example of the most typical way in which the tubercle bacillus performs its deadly work. In the majority of cases, the bacilli are inhaled with the air, but may also infect the lungs from the blood carrying them from tuberculosis in other parts of the body. The bacilli are incapable of independent movement. This difficulty is too readily overcome in the body, as the streams of blood and lymph easily carry them along. Their movements in the body may be aided by certain scavengers that are crawling about in our tissues and circulating in our blood; namely, the wandering cells of connective tissue and the white blood corpuscles. These take up the bacilli by wrapping their substance around them; then, for a time, they crawl about carrying with them the bacilli. In this attempt to devour the tubercle bacillus, they often find they have caught a Tartar, who in turn feeds and multiplies in them, and thus their wandering days soon end. Many other diseases are known to be caused by bacteria, such as anthrax, cholera, pneumonia, typhoid fever, erysipelas, leprosy, suppuration, and ordinary blood-poisoning. Before Sir Joseph Lister introduced the system of antiseptic surgery, bacteria were a most fertile source of danger in surgical operations by the decomposition and suppuration they set up in the wounds. In this short paper it is impossible to describe the characteristics of any other pathogenic bacteria, but perhaps enough has been written to show the great danger to which we are exposed from attacks by an immense army of minute foes. FOREST FORMATIONS --M. J. SCHLEIDEN