One of the first things that the United States Government did in beginning work in the canal zone was to take up the fight against the yellow fever mosquito. In Panama where the water for domestic purposes was kept in cisterns and water-barrels, inspectors were appointed to see that all such receptacles and other possible breeding-places for mosquitoes were kept covered. After the first inspection, 4,000 breeding-places were reported. About six months later there were less than 400. Similar work was done in all the towns and settlements along the route of the canal. In addition to this fight against the yellow fever mosquito considerable attention was paid to the breeding-places of the malarial mosquito. The results have been remarkable. Cases of yellow fever are now rare throughout this zone, and there has been a very great reduction in the extent of the malarial districts. The last case of yellow fever occurred in May, 1906. Before this work was done a man took his life in his hands when he went into this region. Now it is regarded as a perfectly safe place to live. Indeed it is a much safer place than many sections of our own country where proper sanitary measures have not been taken to protect the health of the community. IN RIO DE JANEIRO In Rio de Janeiro they have as yet been unable to get rid of the mosquitoes, although thousands of dollars are spent annually in fighting them. But the non-immunes there protect themselves by doing their business in Rio during the day and going back at night to Petropolis, twenty-five miles inland and twenty-five hundred feet higher, where they are safe, for no _Stegomyia_ have ever been found there. They claim there that the yellow fever mosquito does not bite during the daytime after she has laid her eggs, and that she will not lay her eggs until about three days after she has fed on blood, therefore a _Stegomyia_ that bites during the day will not carry the yellow fever because she is too young. This seems to explain why the fever cannot be contracted by being bitten by a mosquito in the daytime. Certain other experiments, however, have given different results so that as far as we know it is not safe to be bitten at any time by such a mosquito in a region where the disease is endemic or where it is epidemic. In the main the work of the French Yellow Fever Commission working in Rio de Janeiro has confirmed the findings of the American Commission. One interesting special thing that the French Commission seems to have established is that the female may transmit the infecting power to her offspring, so that it would be possible for a mosquito that had never bitten a yellow fever patient to be capable of infecting a non-immune person. While all this is very probable in the light of what we know of the disease and the way in which other diseases caused by similar organisms may be transmitted by the parent to the offspring, yet the most conservative investigators are waiting for further proof.