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. 5. _The Sea Serpent_ The sea-serpent rarely puts in an appearance now, though a Cornish “manifestation” was reported last year. A recent account of a strange marine monster, declared by some to be, of course, the sea-serpent, seen but to disappear, was that given by Lord Crawford’s companions two years ago. In that case, and in others in which a huge fin-like structure, supported by fin-rays, has been seen projecting from the mysterious animal, it is not improbable that what was seen was a large seal of the “eared” kind, raising one of its long, webbed hind-feet from the water, a trick which some of them are known to have. Other reputed sea-serpents have been, in reality, a school of porpoises, or a line-like flight of sea-birds, or a mass of seaweed, or a whale in association with one or other of these--or, again, a real marine snake 5ft. long (such are well known and very poisonous), or a ribbon-fish 12ft. long. There is “no reason why there should not be” a huge and seldom-seen kind of animal living in the sea--like a serpent in appearance. No one can say, as the result of observation, that there is not, since no one has thoroughly explored the dark, unfathomed depths of ocean. Yet we gain very little when we have admitted our ignorance, and agreed that there is no reason why something should not be. The real question is, “Does the thing in question exist?” not “Could it possibly exist?” Does the great sea-serpent exist? The answer to that is, There is not much evidence to show that it does. Most persons who have looked into the matter would be willing to bet 100,000 to 1 against its being captured, dead or alive, and brought before the Royal Society within ten years’ time. Unless it be so captured and “tabled” it matters very little whether it exists or not. It must be “discovered” in order to become really interesting. 6. _Giraffes and the Okapi_