At the end of twenty minutes, Ashton-Kirk took the bit of glass from the fixing bath, threw the alcohol into a waste pipe and ran some water into the vessel.
"It will take some ten minutes for the slide to dry," said he. "And in the meantime we shall prepare the next step in the process."
He took down a bottle filled with a dark blue liquid. This he held up to the light that poured in from the window.
"Here," said he, "is the bloodhound upon whom I depend to find and mark the parasite. It bears the rather formidable name in its present state of aqueous methylene-blue, and is in a two per cent. solution. Combined with it is a five per cent. solution of borax. I had a druggist send it in this morning."
This mixture he poured into the small vessel until the bottom was barely covered; then he added water until there was a layer of perhaps one centimeter in thickness, and the blue began to become transparent.
The alcohol had dried off the bit of glass by this time; and Ashton-Kirk took the fragment up with a pair of forceps and dipped it several times into the methylene stain; after this he passed it through clear water until the blue paled to a greenish tinge. Then he took up a white disc of filter paper; placing this upon a stand he laid the glass upon it and carefully dried both sides, much as one would blot ink from a letter sheet.
"This process is what is called staining," said Ashton-Kirk, "and the method I have used is one recommended by Koch; it is somewhat similar to the older one of Mannaberg, but more rapid in result."
Out of a tube he dropped a single gem-like globule of cedar oil upon the blood smear; then he covered it with a small square of glass; upon this in its turn fell a second drop of the oil.
The whole was then placed in position under a microscope and fastened. Then the secret agent brought out the lens. It glittered like a tiny diamond in a huge setting, and Fuller gazed at it fascinated.
"How you can see anything through a glass as small as that I can't understand," said he. "It looks like the point of an awl."