It has been stated that the products of indigestion in the bowels are (a) gases and acids, (b) toxins. The former have been considered. It has also been shown why auto-intoxication does not constantly occur. We must now state the conditions in which autointoxication does occur, the consequences of it, and what can be done to prevent it.

The causes of auto-intoxication are many; several of them have already been dealt with. They are: (a) The com-sumption of too much protein food, or such foods in an unsound condition; (b) a defective action of the nervous system, leading to a failure of the processes of digestion, torpidity of the bowels, constipation, fermentation, and putrefaction within the alimentary canal; (c) dilatation of the stomach and hypochlorhydria; (d) duodenal atony and catarrh; (e) atony and catarrh of the small or large intestines. Moreover, there may be a failure on the part of those organs whose duty it is to destroy or eliminate from the body the toxic products of digestion. When the bowels act in an ordinary manner, they carry away from the body a large amount of the toxic materials produced during digestion, including leucomaines and ptomaines. Constipation, which is one of the symptoms of intestinal indigestion, therefore tends to the absorption of poisonous materials and auto-intoxication. The liver normally destroys any leucomaines, ptomaines, purins, and other poisonous bodies which are absorbed; but the amount absorbed may be too great to be disposed of in this way; or the functions of the liver may be disturbed, and in either way auto-intoxication will arise. The kidneys usually excrete more than two-thirds of the total amount of waste materials absorbed from the alimentary canal or produced by the processes of metabolism. These substances include urea, uric acid, purins, indican, sometimes leucin and tyrosin, colouring matters, and mineral substances. The skin eliminates water, salts, a little urea, and those volatile and poisonous bodies which give a characteristic odour to some persons. The lungs excrete, besides water, carbonic-acid gas and other gases, certain substances of the indol group, which, if they are in abnormal amount in the blood, give an unpleasant odour to the breath. Thus we perceive that autointoxication is due to excessive production of poisonous substances in the alimentary canal and, when the organs of excretion are disturbed, defective elimination of these substances.

The commonest symptoms of auto-intoxication are those of intestinal indigestion previously mentioned - viz., indigestion, bilious attacks, headache, migraine, vertigo, neuralgia, neurasthenia, general debility, and other symptoms detailed in connexion with disturbance of the gastric and intestinal functions in the preceding sections.

The consequences of auto-intoxication are numerous and may be classified as follows : (i) Neurasthenia, polyneuritis, migraine, insomnia, hypochondria, and many other nervous complaints ; (2) disturbances of the nerves which govern the circulation, especially causing palpitation and irregularity of the heart, pains in the cardiac region (false angina and other cardiac neuroses), cold hands and feet, etc.; (3) chronic bronchitis and asthma; (4) gout, rheumatism, and rheumatoid arthritis; (5) skin diseases, such as chronic urticaria, erythema, acne rosacea, eczema, etc.

Many of these diseases are associated with a steady and persistent auto-intoxication; so long as the toxins are absorbed, the disease remains; when the auto-intoxication is stopped, the disease tends to get well. But probably no part of the system is more affected by the absorption of toxins than the heart and blood-vessels. The multitude of alimentary poisons has been divided into two classes: (a) those which have a relaxing effect on the vessels, and lower the blood pressure (hypotonus); (b) those which constrict the blood-vessels, and raise the blood pressure {hypertonus). The poisons, being absorbed into the blood, circulate through the vessels to all parts of the body ; but they affect the tissues of the blood-vessels just as they do other tissues. Some of them relax these tissues and cause the low blood pressure, indicated by a soft and compressible pulse; others by their constant presence irritate the coats of the vessels, and such irritation leads to new cell-formation and thickening of the arteries or arteriosclerosis, indicated by a firm and incompressible pulse, which becomes more or less like whipcord. Such poisons increase the blood pressure. When an infusion made from decomposing meat is injected into the blood, the tension of the vessels is speedily increased, as it is by ergot, digitalis, and adrenalin, and remains so until the toxins have been destroyed or eliminated from the system. In fact, the most pernicious toxins which enter the body arise from the decomposition of protein foods; and those arising from animal proteins are said to be more poisonous than those of vegetable origin. A noted physician has said that every particle of protein consumed above 70 grammes daily is reduced to leucin, tyrosin, indol, skatol, phenol, cresol, muscarin, cadaverin, pepto-toxin, neuridin, neurin, cholin, mydalein, and special toxins from particular foods - e.g., tyrotoxicon from cheese, gadin from codfish, scombrin from mackerel, etc. There is no doubt about the production of these poisons in the body; but it is very doubtful whether everybody at all times produces such toxins whenever more than 70 grammes is consumed. On the contrary, there are many people who can safely consume twice that amount without suffering from toxaemia; and it is equally certain that many people who consume less than 70 grammes a day suffer from toxaemia and present well-marked signs of auto-intoxication.

The treatment of auto-intoxication consists of preventing the absorption of toxins from the bowels, and promoting their elimination by the various organs of excretion. It is necessary to determine in each case what conditions exist likely to favour auto-intoxication. An inquiry into the amount of protein consumed will settle the question of excessive consumption. The gastric and intestinal functions will next be examined; dilatation of the stomach and hypochtorhydria will be sought for; duodenal and intestinal catarrh ; deficiency of nerve power or control over the digestive processes and movements; and deficiency in the elimination of waste products will be determined. Each of these conditions requires the treatment appropriate to it.