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 origin of the scleroses which engender chronic diseases, we find that they are due to the action of various poisons, among which syphilitic poison and the immoderate use of alcohol take the first place. These are also the usual causes of senile degeneration. But there must be some other, some very general cause to explain the universality of the process of senescence. Metchnikoff thinks that he has found this cause in the microbes which swarm in man's digestive tube, particularly in the large intestine. Their number is enormous. Strassburger has given an approximate calculation, but words fail to express it. We have to imagine a figure followed by fifteen zeros. This microbic flora is composed of "bacilli" and of "cocci," and comprises a third of the rejected matter. It produces slow poisons, which, being at once reabsorbed, pass into the blood and provoke the constant irritation from which results arterio-sclerosis and the universal sclerosis of old age. Instead of enjoying a healthy and normal old age, in which the faculties of ripening years are preserved, we drag out a diminished life, a kind of chronic disease, which is ordinary old age. This is due, according to Metchnikoff, to the parasitism and the symbiosis of microbic flora, lodged in a part of the economy in which it finds all the conditions favourable to its prolific expansion. Such is the specious theory, held to the verge of intrepidity, by which this investigator explains the misery of our old age, and which inspires him with the idea of a remedy. For his observations conclude with a régime, a series of prescriptions by which the author fancies that life may be lengthened and the evils of old age swept from our path. The dangerous flora