I am inclined to attribute our freedom to the way in which we killed the mosquitoes. We have fifty men at this work, oiling and draining small collections of water in every house and putting oil in all the sinks and closets so that it will run down into the cesspools. During the winter and cool periods of the year, up to this time say, the cesspools are the great places for breeding mosquitoes. All the cesspools, so far, have larvæ in them; when water barrels and cisterns in same yard have none. I am inclined to think that Dr. Guiteras, and other mosquito breeders, would get much more vigorous larvæ if they would use blood or some richer food than mere bread. We have been trying them side by side and find that sewer water develops much more hardy and large larvæ than rain water with bread alone in it. I have had all the little streams and ditches in the suburbs cleaned and oiled; and we have killed a great number of larvæ. You can go to any sewer mouth now and see the dead larvæ running out in considerable numbers, coming principally, I think, from the fosomauros, where they have been killed by the oil which would no doubt remain upon them for several hours. But we have evidently had some tough old infected fellows, who have hibernated through the winter. For instance, on the two cases that occurred on the 21st and 22d of April (in different parts of the city, however), the mosquitoes were killed as thoroughly as we knew how. Every room in the house was closed; and a pound of pyrethrum powder burned to 1,000 cubic feet, and oil used everywhere, sewers and everywhere else. Not only was this done in the infected house, but in the fifteen or twenty contiguous houses. On each case we used 50 pounds of pyrethrum powder and something like 40 gallons of oil. I think the results show that we probably got hold of the infected mosquito or mosquitoes. We did the same thing on May 6th and 7th; and it now looks as though we had gotten hold of the infected mosquito there. The prospect of getting infected mosquitoes now is poor. So far we know of none in Las Animas; all the cases this year having been exceedingly mild. It takes a Board with decided “amarylic” to diagnose them. Would like very much to see you, Durham and Carroll down this summer, that is if you did not object to coming. Dr. Gaylor, of the New York Pathological Laboratory, wants to take a whack at yellow fever, after his success at cancer. He asked me to let him know when I could get him some more autopsies of yellow fever, and he would come down at once. We have things nicely fixed at Las Animas now; and I think we would do good work if we only had yellow fever; but of course we can do nothing if we don’t have. Mrs. Gorgas has just returned from the “States” and joins me in kindest regards. I got weak in the knees and was afraid to keep our small girl down here, even though we had no infected mosquitoes. Very truly yours, W. C. GORGAS. (3)