The genetic aspect of tubercular diseases has been studied for a long time, using the genealogical method, which had forerunners even in the field of narrative, where some Authors, such as Emile Zola, described families in which there was a high frequency of tuberculosis. Then, many Authors gave scientific descriptions of genealogical trees largely stricken by this disease, demonstrating the necessity of stating this problem: Although tuberculosis is originated by a microbe, it can also derive from a particularly receptive, inherited ground. The statistical research, in the hands of Person, Govaerts, Pearl, Ickert and Benze, Geissler and others, indicated that the question was legitimate and that the answer must be positive, because the probability of being affected by tuberculosis is four times higher when the parents, instead of being healthy, both have the disease; because among the ascendants of tuberculous people one finds six times more affected individuals than among those of healthy subjects; and for other similar reasons.

Then, the twin method, used by v. Verschuer, Diehl and Mittschrich, Kallmann and Reisner, by Heilinger and Kunsch, by Vaccarezza and Dutrey, by Kallmann and Jarvik and by others, emphasized the hereditary factor in tubercular diseases.