Professor Elias Metschnikoff was busy, when I saw him at the Institut Pasteur in Paris last September, with an experimental investigation of “appendicitis.” He finds that chimpanzees can exhibit this disease, and he is led by experiments on those animals to believe that a gas-producing micro-organism—the bacillus aËrogenicus—already known as occurring in the human intestine—is especially active in exciting the disease. Parasitic worms or other foreign bodies must first wound the delicate lining of the appendix before the virulent gas-forming bacillus can penetrate and start inflammation and abscess. Metschnikoff was also investigating a disease of tropical regions, known as “the Yaws.” Most people would imagine that this name refers to a disease like the gapes, but it is quite different, being an ulceration of the skin caused by a spirillum.

Spirilla—corkscrew-like threads of excessive minuteness—are parasitic organisms, like bacteria, bacilli, and micrococci. They are of different kinds—some harmless, some deadly. One is common in the mouth of the healthiest of us—another causes one of our most terrible diseases. They can be distinguished by the microscope, though much alike. What microscopists call “dark-ground illumination”—that is, illumination by horizontal rays of light, obtained by a prism attached below the glass slip on which the object is placed for examination with the microscope, has been found at the Institut Pasteur to be a very ready way of showing the spirilla in fresh blood or sputum. The spirilla are alive, and are seen when highly magnified, shooting rapidly across the field of view with a corkscrew action, like brilliant silver threads. The detection of the microbe which causes an infective disease, is often the first step to the control of the disease, or to knowledge which enables man to avoid the disease altogether. Some striking examples of this have occurred of late years.