The hereditary factors are regarded as being less influential at the present day than was held prior to Koch's important discovery of the tubercle bacillus. It has been conclusively shown that direct hereditary transmission is an exceptional occurrence. Hauser, in an extensive and careful review of all previous work upon this question, reached the conclusion that there are only 18 authentic instances of direct inheritance of this disease to be found in the literature. In all of these cases only the mother had tuberculosis. He contends that conclusive proof of direct transmision from the father is wanting and this position is probably the correct one. Hauser attempted to produce experimental direct hereditary transmision in guinea-pigs and rabbits, and in a single animal only was he successful, and this had been kept alive for months after birth. He decided that the theory of direct inheritance rests on insufficient evidence.