There is a resistance to tuberculosis in human beings which is called immunity. Most people possess it in some degree, but some to a much greater degree than others. Some races possess it in a greater degree than others and some families possess it in a greater degree than others. The probabilities are that immunity is gradually developed by resistance to the disease, and that for this reason families and races which have been fighting the disease in some of their members for long periods have great resistance. Children born of tuberculous parents are apt to have more immunity than the parents had, and when the disease has been in a family for three or four generations those who have withstood it usually have a very great immunity. Of the various races the Jews have the greatest immunity. There is no permanence in immunity against tuberculosis in the individual, the family or in the race. It may be lost after many generations in the family and it may be lost in the individual through depression in health. Racial immunity is probably the most durable of all.