In the auto-toxic etiology of diseases of the skin two elements are of importance, - the nervous and the vascular. The nervous because the peripheral nerves are everywhere present in the skin, and impulses generated centrally may elicit responses at the most remote parts of the body. The vascular, because toxic materials may be borne in the blood stream to every part of the body visited by the circulation, and have a local effect anywhere in the vascular system, but particularly in the capillaries where the blood current is slowed. The cellular changes which take place in nerve paths in chemical poisonings indicate that similar changes probably take place in autogenous poisonings and these result in the impairment in the functional activity of the neurons which necessarily causes trophic and vaso-motor changes.

It is well known that disorders of the digestion are very frequently accompanied or followed by cutaneous eruptions, and these are due to auto-intoxication if the poison is formed within the body, but are extrinsic if it is ingested preformed. For this reason shell-fish and food poisoning will not be discussed.

We shall see that auto-intoxication causes a great variety of mental symptoms varying from slight indisposition to delirium and coma. It is well known that the insane and mentally depressed are particularly liable to skin diseases, and it is quite reasonable to suppose that the same cause may in many cases act as the cause of both disorders. The probability of these views is increased by the fact that the most helpful drugs in skin diseases are those which stimulate the, nutritive processes, increasing oxidation and enhancing the action of the emunctories.

Constipation, the bete noir of modern strenuous life, is undoubtedly the cause of many cases of eczema, acne, erythema and dermatitis, for these frequently disappear when the lower bowel is regularly relieved by enemata or when the disorder is corrected by suitable diet. Degenerations, infectious granulomata, and neoplasms cannot be attributed to auto-intoxication which produces erythemas and angio-neuroses of which urticaria is the type.

Of the neuroses, pruritus and anesthesia may. be traced to intrinsic poisons.

In urticaria, through the action of intestinal poisons, the nerve cells of higher centres are irritated, efferent impulses are sent from the vaso-motor centres to the peripheral vascular nerves, momentary contraction is first caused and then paralytic dilitation ensues. This causes blood stasis with serous effusion and even corpuscular extravasation.