Shortly after, Ricketts and Wilder (1910) succeeded in transmitting the disease to the monkey by the bite of body lice in two experiments, the lice in one instance deriving their infection from a man and in another from the monkey. Another monkey was infected by typhus through the introduction of the feces and abdominal contents of infested lice into small incisions. Experiments with fleas and bed-bugs resulted negatively. Subsequently, Goldberger and Anderson (1912_b_) indicated that the head louse (_Pediculus humanus_) as well, may become infected with typhus. In an attempt to transmit typhus fever (Mexican virus) from man to monkey by subcutaneous injection of a saline suspension of crushed head lice, the monkeys developed a typical febrile reaction with subsequent resistance to an inoculation of virulent typhus (Mexican) blood. In one of the three experiments to transmit the disease from man to monkey by means of the bite of the head louse, the animal bitten by the presumably infected head lice proved resistant to two successive immunity tests with virulent typhus blood. In 1910, Ricketts and Wilder reported an experiment undertaken with a view to determining whether the young of infected lice were themselves infected. Young lice were reared to maturity on the bodies of typhus patients, so that if the eggs were susceptible to infection at any stage of their development, they would have every opportunity of being infected within the ovary. The eggs of these infected lice were obtained, they were incubated, and the young lice of the second generation were placed on a normal rhesus monkey. The experimenters were unable to keep the monkey under very close observation during the following three or four weeks, but from the fact that he proved resistant to a subsequent immunity test they concluded that he probably owed this immunity to infection by these lice of the second generation. Anderson and Goldberger (1912_b_) object that due consideration was not given to the possibility of a variable susceptibility of the monkey to typhus. Their similar experiment was "frankly negative." Prophylaxis against typhus fever is, therefore, primarily a question of vermin extermination. A brief article by Dr. Goldberger (1914) so clearly shows the practical application of his work and that of the other investigators of the subject, that we abstract from it the following account: "In general terms it may be stated that association with a case of typhus fever in the absence of the transmitting insect is no more dangerous than is association with a case of yellow fever in the absence of the yellow fever mosquito. Danger threatens only when the insect appears on the scene."