From the library one naturally passes to the laboratories. They open from the long halls in numbers. One wonders how so much room can be utilized, but none seems to be going to waste. In each some step of the microbic process is going on. Here is a doctor inoculating a rabbit with the poison of a mad dog sent to the Institute only the day before. The little animal lies on the table insensible, chloroformed, while with the sharp-toothed little trephine the operator makes a tiny hole in its skull, lays bare the brain, and inserts the virus. By the time the aperture is closed Brer Rabbit is sitting up, looking about, none the worse for his experience, save a bald spot on his forehead, a tiny tin tag covered with hieroglyphics hanging from his ear. Two minutes later he was nibbling a carrot; fifteen days later he died "mad as a March hare." It is not only rabbits which undergo this operation. Guinea-pigs, chickens, mice and rats are used in quantities. In the laboratory of autopsy there are to be seen aquariums filled with the dainty axolotl of Mexico, glasses of odd fish, even cages of birds. In another room an experimenter is dissecting a rabbit which has died of rabies, and from whose spinal cord he expects to get material for vaccinal virus. [Illustration: DR. METCHNIKOFF IN HIS LABORATORY.] In a small dark room, whose temperature is never allowed to vary, which is never swept nor dusted for fear of arousing tranquil microbes, and whose door is never opened except when absolutely necessary, are arranged rows of drying bottles, in which hang bits of the marrow. These bottles are marked with the degree of violence of the rabies from which the animal died, and with the date when the marrow was put up to dry. Here, attendants are preparing the veal broth and the gelatines in which the infected marrows will be cultivated. [Illustration: FILLING THE SYRINGES.] Thus as one goes from room to room he can follow the whole method of successive cultures, that method which is "the key-stone of the arch, and without which there could be no vigorous demonstration of the Pasteur method." On every hand one sees the interesting "ways of doing things" which characterize the Institute. Here, the cleaning of jars, syringes and tubes is going on; not a simple washing and drying. In the Pasteur household articles are sterilized as well as cleaned--that is, burned in the flames of a spirit lamp, or in an oven. There, a man is blowing bulbs, droll balloon pipettes, all the multitude of glass contrivances the laboratories demand. Here, under a microscope, an investigator has the diphtheria pest, an inoffensive speck; there, another has in his field a whole colony of lively little straight and bent sticks; it is a company of Doctor Koch's cholera microbes.