The Effects of Disease. In the case of nearly all infectious diseases, the effects on the nervous system are among the last to appear, and may not occur until weeks, months, or even years after the main fever or attack of sickness. This is one of the reasons why, when they do occur, they are often hard to cure; the whole system has become saturated with the poisons before they reach the nerves at all. So it happens that the idea has grown up that nervous diseases are very hard to cure. When, however, we know that two-thirds of them are a late result of some of the preventable infectious diseases and fevers, we can realize that it is perfectly possible to prevent them, and that prevention is the best cure. The poisons that attack the brain and nervous system may be formed in the body by disease germs or brought in from without, as are alcohol, tobacco, lead, or arsenic. Even such mild infections as measles, scarlet fever, and influenza may poison certain nerves supplying the muscles of an arm or a leg, causing temporary paralysis, or even permanent laming; or they may attack the nerve of sight or of hearing and produce blindness or deafness. A great many of the cases of paralysis and insanity are caused by alcohol. Alcohol in excess may attack the nerves supplying the arms and legs, producing severe pain and partial paralysis. It may also, after long-continued use, affect the cells of the brain itself, producing the horrible condition known as delirium tremens--a form of acute insanity with distressing delusions, in which the patient imagines that he sees rats, snakes, and other reptiles and vermin crawling over him, or in his room. Even in those who never use it to such excess as this, or indeed in those who may never become intoxicated, the long-continued use of alcohol may produce a slow poisoning and general breaking-down of the whole nervous system, causing in time the hand to tremble, the eye to become bleared and dim, the gait weak and unsteady, the memory uncertain, and the judgment poor.