In this study we are proceeding along the same road we follow in investigations concerning other diseases. In a philosophical sense, there lies back of all manifestation of diseased action, an antecedent condition, which is the soil from which morbid actions spring. There exist the scrofulous, the phthisical, the gouty, the rheumatic diatheses, and, hence, the question of heredity is of the utmost importance in reference to many forms of disease. "To many intents and purposes, we are born one generation at least, and generally more, before we come into the world. The soil whence the protoplasm of our grandfathers was formed, has a large significance in reference to ourselves. We limp, because they were gouty; we groan with rheumatic pains, because they slept in damp rooms; the neuralgic twinges of their fifth pair of nerves extend over into ours. The acid of the grapes, which our fathers ate, has acted on the enamel of our bicuspids and molars. That intangible tendency to weakness, to unhealth, so indefinable, so delicate, so inappreciable to our senses, is yet the mightiest factor in our being, and measures the amount of our physical pains and sufferings with a greater delicacy than we have been wont to think. It is the match, which needs only to be rubbed,--or the tinder waiting for the spark,--or the acid for the alkali. On no other theory are we able to explain the effects, or absence of effect, from the exciting causes of disease. For instance: in one case cold produces neuralgia, in another rheumatism, in another pneumonia, in yet another bronchitis, and in the fifth person no morbid action at all. Now in these several persons there must have existed a primary or induced condition of the several parts affected, of such a nature, that a common cause, acting upon all alike, yet produced widely different results.