The acute and chronic contagions and infections so lower cell vitality through the perverted functions described that inert connective tissue replaces healthy working cells. This is especially the case with syphilis, which, when driven from the system, leaves behind it a tendency to disease based on this connective tissue increase. This tendency, latent in the ancestor, may be so intensified in the descendant as to produce the hereditary ataxias (loss of movement power), and like neuroses. At the periods of stress such tendencies are peculiarly potent, and not only check, but reverse development. The chronic contagions and infections are most fertile sources of human degeneracy since their weakened products are enabled to survive under modern beneficence. Of these chronic contagions two (tuberculosis and syphilis) alone deserve attention, since the third (leprosy) exerts but little influence. Despite its existence for more than a century (New Brunswick and Nova Scotia on the north and Louisiana on the south) on the borders of the United States, despite its subsequent importation from Norway, Sweden, China, and Hawaii, its spread has been infinitesimal, and its influence on race deterioration is still less demonstrable. Tuberculosis ("the white death") is from every standpoint a social danger more serious than syphilis. The father, as in syphilis, can infect the mother, but sterility is much less likely. As has already been shown in the chapter on heredity, plural and quickly repeated birth are common in tuberculous families. The tuberculous diathesis (or "habit," as Weismann calls it) was very early observed in the United States. Nearly seventy years ago W. P. Dewees, of Philadelphia, pointed out its frequency and its early observation by the Greek and Roman physicians. He cites a case illustrative of the extent and uniformity of diathesis in a very numerous family. This predisposition arose on the side of the mother, though she lived herself to the age of forty-three, a period much exceeding that of any of her children, with the exception of a son, who died in his forty-fifth year. This lady bore twenty-three children without being able to suckle any but the two first. The males much exceed the females in number, yet there did not appear to be any exception to their favour in the transmission of the phthisical taint, except that they attained in general a greater age before they died. Some died about puberty, others at manhood or womanhood; but all, with the exception just stated, under thirty. The disease was never very rapid; they generally complained from one to two years before they died. The men had a healthy, even in some instances an athletic, appearance until the disease became open and decided. In their growth and stature they altogether resembled the father, who was not only a remarkably stout man, but lived beyond the eightieth year. The females, who passed puberty (two in number) were rather stout