Potassium iodid has a very destructive effect upon the natural functions of the body, and for this reason it has been associated with mercury in the treatment of syphilis, the usual method being to alternate between potassium iodid and mercurial salts. LEAD AND COPPER The salts of lead and copper, like those of mercury, are poisonous. However, these salts are not extensively used in medicines. The mineral acids, such as sulfuric, are recognized poisons, but their destructive effects upon the living tissue are so apparent and so painful that they have never gained favor with physicians. PURGATIVES AND CATHARTICS [Sidenote: Effects of salts] The popular term "salts" includes sodium sulfate (Glauber's salt), and magnesium sulfate (Epsom salts). These salts cause a large amount of watery mucus to be excreted from the mucous membrane of the intestines, the physiological purpose of which is to wash the offending substances from the body, thus producing a laxative effect. Were the large doses usually taken of these salts absorbed into the blood, death would ensue within a few hours. The number of products that are used for the purpose of relieving constipation is almost unlimited. Many poisons which react directly upon the mucous membrane of the alimentary canal have a laxative effect. [Sidenote: Why laxatives cause loss of vitality] Laxative drugs do not act on the body--the body acts on the drug because it abhors a poison, and, in throwing out the drug, the food residues of the digestive tract are also thrown out, regardless of whether digestion is complete or not. The rapid loss of vitality and weight while taking physic is caused by this fact. [Sidenote: Object of this lesson] In this lesson I have examined only a few of the many thousand drugs in general use. I have omitted many drugs and compounds whose properties and uses would form interesting information, but the purpose of this book is to impart a knowledge of foods, not a knowledge of drugs. This lesson, however, is for the purpose of giving the reader some authentic information about the standard drugs and medicines, so that he may form his own conclusions in regard to the efficacy of drugs in curing dis-ease. If the reader will secure at a public library a copy of the "National Standard Dispensatory," the book used by practising druggists, and scan through its two thousand pages, he can form some idea of the limitless number of things, and the complex, uncertain, and unscientific methods used in the prescribing and in the dispensing of drugs. LESSON X IMPORTANCE OF CORRECT DIAGNOSIS AND CORRECT TREATMENT The word "diagnosis" is derived from two Greek words, "dia," meaning _through_, and "gnosis," meaning _knowing_. It therefore means literally "through knowledge," "to know thoroughly," or, as we now say, "thorough knowledge." The old form of the word is still retained in the very common expression "to know it through and through."