Thread-worms live in the lowest part of the bowel, and so cause much itching and tickling about its orifice. This prompts the child to scratch itself, with the result that some of the innumerable eggs laid by the worms adhere to the fingers, and once there soon find their way, along with the fingers, into its mouth. The intruders are usually easily expelled by an injection of salt and water, but it is difficult to get rid of all of them, and the child is nearly sure to reinfect itself unless it is made to sleep in drawers. Provided reinfection is prevented in this way, however, the remaining worms will soon be got rid of, as this species as a rule does not take up a prolonged residence. Round-worms can be expelled by the means of a dose of santonin, but as neither these parasites nor tape-worms usually cause immediate serious symptoms, and both this drug and most other vermifuges require a certain amount of care and caution in their administration, it is better to wait any moderate time until the treatment can be supervised by a medical man. The third common round-worm parasite--the hook-worm namely--though but little known in Europe, is so widely distributed in hot, moist countries, that in such climates the greater proportion of the indigenous races are often affected to a greater or less extent. It is quite a small worm, but fastens on the lining of the bowel in exactly the same way as leeches attack the outer integuments, and exhibits the same insatiable appetite for blood. The extent of the mischief wrought by them depends entirely on the number harboured. When only a few are present, they may be considered practically harmless, and thousands of such cases are to be met with in any country where they are common; but wherever this is so, numbers of subjects will be met with, in whom they are so numerous as to cause serious symptoms and death; so that there are many places where they constitute one of the most serious scourges of the Tropics. The eggs of this parasite, deposited along with the dejecta of persons infested with them, hatch out in the soil, and multiply there enormously, so that owing to the insanitary habits of the populace, the soil round about a native village comes to swarm with this free stage of the parasite. Now as the population is generally a purely agricultural one, and none too nice in its habits, it can be easily understood that persons, eating as they do with unwashed hands, must constantly carry to their mouths some of the earth containing the minute embryos which convey the disease, and hence the process of infection is commonly continuous and progressive. As a matter of fact, out of some hundreds of specimens of drinking water examined by the writer in Assam, where the disease is extremely rife, in no one case was there anything found to show that the malady was commonly conveyed in water, but the contingency is clearly a possible one; and in any case, it is clear that