“The wicked flea,”—Everybody knows the “wicked flea,” for it is no respecter of persons. It makes its home in the palace of the prince, the hovel of the savage, and the tent of the Arab. The devotions of many a worshipper are destroyed by the Pulex tabernaculi, or church flea, which makes up by its voracity on Sundays for enforced abstinence on other days of the week; and one of the wonders narrated by travellers is that on camping in the desert they have found this wicked little creature waiting for them, ready to bite, although apparently its progenitors from time immemorial could hardly have had an opportunity of gratifying their taste for blood. When in Rome one summer, fleas were abundant in the hotel where I was staying. I used to walk barefooted about my room every morning, and soon a prick on the instep would warn me that a flea was there. I looked down, saw a little black speck, put a wet finger upon it, and after a little rub would transfer it to a basin of water. The sensation of something solid between the finger and thumb and the transference of the black speck from my instep to the water convinced me of the presence of the flea, for I had the threefold evidence (1) of common sensation, (2) of sight, and (3) of muscular sense all combining to prove the actual existence of the flea. At other times during the day I had the evidence of sensation to indicate to me that fleas were again biting, and I felt quite convinced by sensation alone that such was the case, for although I could not corroborate the evidence of sensation either by sight or by muscular sense, yet it was not contradicted by these senses. But sometimes I have felt upon my hand a sensation exactly similar to the bite of a flea, and yet, as the hand has been on my writing-table within full vision, and no object whatever was to be seen on the hand, I have discarded the evidence of sensation in favour of that afforded by sight, and come to the conclusion that no flea either was or had been upon my hand. Had it not been for the sensation of sight, however, and had the hand been hidden from my view, I should have confidently believed that it had been bitten, trusting to the evidence of sensation, which, though unconfirmed by sight or muscular sense, was not contradicted by these senses.