We floated down to the laboratory, and the ghost took from the shelf a wide-mouthed bottle and held it up to the light. "Here," he said, "we have a culture. You, of course, understand how the germs of disease are cultivated for experimental use. It is needless for me to explain to you that certain media are used for these cultures, such as milk, beef-broth, etc. "Here we have the germ of diphtheria, here of tuberculosis, here of typhoid fever, etc. That little short jar over yonder contains some cholera bacilli, which have been lately sent here. Now look at this typhoid germ. If we took a drop of healthy blood and put some of these typhoid germs in it, how they would wiggle! but if the drop of blood was from a typhoid patient, they won't wiggle very long, as you know. See this blunt-headed chap which we have to stain to see properly, even with this wonderful microscope; that is our old friend the bacillus of tuberculosis; but unless you see the patient first I do not believe you could distinguish him from the leprosy bug. "These are known germs, but look through the glass at this drop, and you will see some bugs worth seeing, although the medical fraternity have not as yet discovered their value. Perhaps you know that most bacteriologists consider these germs to be plants, not bugs, although they admit some of them move a little. How astonished they would be if they could look through this glass! See that chap with green hind legs: he preys on the typhoid germ, and when they discover this physicians will simply inoculate the patient with a lot of these little chaps with the green legs, and they will do the rest. "Here is a germ with yellow stripes which looks a little like a diminutive potato bug. He is the deadly enemy of the bug of consumption, and will attack and kill him on every possible occasion. They are about evenly matched, but I think the little striped chap is a bit the better. Another ghost and myself made a match the other night,--seven battles, the result to decide the championship,--a sort of a bugging main, as it were. I won. The first six matches were even. We won three each, but in the seventh my striped bug got the tubercular germ down and shook him as a terrier does a rat. The other ghost and myself nearly had a fight to get our eyes to the microscope. I tell you it was exciting. There is my champion bug now, see him?--the one with the fourth hind leg gone." "But how," I asked, "are you going to prevent people from dying of old age?"