It is recognised, however, that the protein molecule and the intestinal juices are liable to putrefaction in the intestinal canal, with the production of fatty acids, ptomaines, and leucomaines (with their secondary products of decomposition, neurin and muscarin), and many aromatic bodies of the nature of phenol, indol, skatol, etc.

Indol, in particular, is the result of the microbic intestinal putrefaction of the proteins, the precursor of which is tryptophane. This was clearly established by Hopkins, the discoverer of tryptophane, and more recently by Underhill in an elaborate research, during which he elicited the interesting fact from a clinical point of view that gelatine does not contain the tryptophane group, and its administration causes a diminished formation of putrefactive products. Hence the indol in the colon and the indican - or, to give it its full name, indoxyl sulphate - in the urine, which is the subsequent form in which it is excreted, are reduced in amount. It is a remarkable fact that indol may even be found in the lower part of the small intestine should any stasis or obstruction arise. An observation which has frequently been made is that indol is formed during starvation, and this has been specially demonstrated during the fasting experiments of Cetti and others. Some have attributed this to the autolysis of the tissues, but on the whole the explanation is considered to reside in the fact that haemorrhages arise during starvation, and the blood thus exuded, in addition to the intestinal juices, undergoes microbic putrefaction.

It is averred that these toxins are absorbed by the intestinal mucous membrane, and that they are the insidious cause of the most grave and fatal chronic maladies. Catarrhal diseases of every form, cutaneous eruptions, Bright's disease, hepatic disorder, neurasthenia, hypochondria, apoplexy, arterio-sclerosis, and premature old age are directly traced to the formation and absorption of these toxins found in the intestinal canal.

It is comforting to think, however, that nature has provided the body with many defences against this terrible risk of poisoning, the most important being the hydrochloric acid of the gastric juice - although it is significant that complete removal of the stomach is unattended by increased putrefaction - and the maintenance of the effective digestive capacity of the stomach and small intestine.

The bacteria of the intestine may be divided into the aerobic saccharolytes which feed upon the fats, starches, sugar, and dextrine, and the anaerobic proteolytes which feed upon albuminous substances. The activity of the former produces acids (lactic, acetic, succinic, butyric, &c), which inhibit the operations of the latter, so that internecine warfare is constantly taking place for the upper hand.

Despite the alkaline secretions of the small intestine, its reaction is acid, owing to the production of the organic acids in the manner just mentioned, and hence little opportunity is given for the triumph of the proteolytes. When, however, any interference with the absorptive capacity arises, or stasis takes place, then putrefaction is apt to occur. Excessive consumption of highly nitrogenous foods like meat, eggs, cheese, etc, especially if not fresh, encourages the anaerobes, whereas careful and slow mastication of abundant starchy foods, with the swallowing of air coincident with this operation, favours the aerobic saccharolytes.

The large intestine, however, is the seat of election for the production of toxins, mainly owing to the fact that it is prone to inactivity and atonicity from our too sedentary existence.

As a rule, in the small intestine the factors just detailed suffice to prevent any trouble, but the colon requires the interposition of the other no less important means of defence, the chief of which is its own mucous membrane. This exercises its protective function not only by its epithelial cells and leucocytes, but also in the outflow of mucus, which hinders the absorption of the poisons by preventing their contact with the living tissue. So long as the mucous membrane of the intestines is intact, little trouble need be anticipated from the ever-present toxins, but when inflamed, as in colitis, or ulcerated, its protective function is in abeyance.

The liver, the thyroid gland, the suprarenal capsule, and the pituitary body are, according to one theory, all possessed of a toxicolytic property which adds to the defences of the body. When these organs fail in their duty it falls to the organs of excretion, the lungs, salivary glands, skin, bowels, and kidneys, to eliminate the poisonous substances from the blood; but the kidneys bear the brunt of the work, with subsequent disadvantage to the integrity of their texture. Given, therefore, a normal individual who neither eats too much nor too often, who keeps his animal food within reasonable proportions, and limits the amount of fluid he consumes at mealtimes, there is little fear of auto intoxication; of this we have abundant evidence in everyday life.

Fascinating as this theory undoubtedly is, and supported by the authority of many capable observers, it does not lack critics of weight who have advanced many objections. Hertz doubts whether indican and ethereal sulphates can in any degree be a measure of auto-intoxication, as "different putrefactive bacteria produce different products, some of which are comparatively innocuous, whilst others are excessively poisonous." In constipation the ethereal sulphates are actually diminished, and so he concludes that there is "no chemical evidence that an abnormal amount of decomposition occurs in the intestines of constipated people." On the contrary, there is reason to believe that there is less decomposition in. constipation, and this would account for the lack of headache in the presence of serious constipation. Yet he admits that the symptoms of constipation are best explained by the theory of auto-intoxication, and is inclined to attribute this variableness to functional or organic disease elsewhere in the system. I can corroborate this statement from a case under my care in which no headache was ever experienced during the most obstinate constipation until after an attack of herpes zoster in the right frontal region, since which time the slightest degree of constipation is presaged by headache in this part.

The rapid relief of a headache which is obtained after the bowels are opened is explained by Hertz on a reflex basis, on account of. irritation of the mucous membrane of the colon, and especially of the rectum, by retained faeces. Kellogg's explanation of this rapid relief is that the liver has a certain degree of toxicolytic power which is exercised with ease up to a certain point, but that even the smallest addition of toxins beyond this limit is accompanied by evidences of toxaemia; the discharge of the mass of toxins in the faeces immediately relieves the strain and reduces the toxins below its destructive capacity. It has been suggested that in prolonged cases of chronic constipation the mucous membrane of the colon has a reduced power of absorption for such toxins.

The arguments in favour of the theory may be criticised, but cannot be refuted, and in the light of the enormous amount of evidence in its favour we must admit the existence of auto-intoxication not only as a fact, but as a factor of immense importance in the incidence of disease. Its malevolent influence is more easily recognised in those exaggerated cases of constipation included under the term chronic intestinal stasis, in which kinks seriously delaying the transmission of the bowel contents occur to such an extent that ample time is afforded for unmistakable putrefaction and decided absorption of the toxins. It is in such cases that the doctrine leaves the realm of theory and assumes an importance sufficiently great to suggest the advisability of such a grave operation as total or partial removal of the colon for relief of the symptoms. Let us hope, with the British Medical Journal, that the "medical and surgical study of disorders of digestion may make so much progress that a rational dietetic system may altogether eliminate the causes of the disorders which to-day medicine uncertainly, and surgery in a more drastic manner, seek to alleviate or cure."