We frequently notice that persons who have not slept well for several nights, especially if passed on a railway journey, look worn out and older. After a good night’s rest these effects disappear and they look fresh and younger again. There are other functional disturbances which are especially harmful as they interfere with the elimination of harmful products either introduced with the food or found in the body (e.g., uric acid). This applies also to the bowels, perspiration, and diuresis. When these important functions are checked, there is retention of poisonous products and a condition of auto-intoxication. These functions are governed by the ductless glands, especially the thyroid, as we have seen in Chapter VI. It is easy to understand that by their interruption the onset of old age is hastened, as these toxins will cause deterioration and destruction of epithelium and the formation of connective tissue in its place. Retained poisonous products play a very great etiological rôle in the production of arteriosclerosis, which is found as a typical symptom of old age in the large majority of aged persons. We thus see that all those agencies which by common consent are usually considered the most frequent causes of old age, are also very detrimental to the ductless glands, especially the thyroid. They produce hyperactivity, with subsequent exhaustion, in these important glands. The pathological and anatomical changes indicating hyperactivity give place to those of atrophy. We have given an example of this in discussing the changes in the thyroid in infectious diseases. The formation of connective tissue is the final result. Thus a condition of the thyroid arises similar to that in myxœdema, which, as we have stated, can be produced by causes similar to those which produce old age—i.e., infectious diseases, exhaustion of the ovaries after pregnancies or sexual excesses, mental emotions, etc. The pathological and anatomical changes in the thyroid, consisting of an increase in the connective tissue, as in myxœdema, will logically produce clinical symptoms, and these symptoms are the same as those of myxœdema. Therefore we are justified in assuming that old age will show the same clinical symptoms as myxœdema. We have shown that, given changes in the thyroid gland, the other ductless glands will be altered too; for instance, the liver and kidneys. These glands have an important function in freeing the organism of poisonous substances. As in old age their secreting elements are more or less atrophied, they are unable to execute their task properly, and these harmful products will accumulate. Now, there are important organs which can act as corollaries to these glands. These are the intestines and the skin. They also are under the influence of the thyroid. In diseased conditions of the thyroid they are unable to perform their functions regularly. The poisons will not be eliminated, and thus a condition of auto-intoxication must arise.