On the 12th of June, 1899, we had had for the month two cases of yellow fever, and in 1900, six. If you consider the amount of work there was to be done, to put oil in all the cesspools, all the water barrels and all the cisterns, once a month, and then keep the streams and pools in the suburbs drained, you will understand that seventy-five men is not at all a large force. I think I could use to advantage more. As you say, we could use less pyrethrum. We arrived at the rate of a pound per 1,000 cubic feet by experiments at Las Animas. We found that in this ratio we could kill mosquitoes in one and a half hours. It would probably be just as well to intoxicate them and sweep them up, and I shall probably cut down the quantity in a short time. We have to sweep them up anyway. But feeling that it may be possible that we have no infected mosquitoes in Havana I want to do everything I can think of, when a case occurs, to increase the chances of killing the infected mosquito in the neighborhood of where the patient got his infection. We are using now from one hundred to two hundred pounds to the patient, killing the mosquitoes everywhere within half a dozen houses of the patient’s home. There is less objection raised to this than to the ordinary disinfection. It damages nothing, only keeps them out of their room for an hour or two, and kills the mosquitoes. I think there is much less opposition to us on this account than there was last year. I feel confident that there is very little concealment of cases, and I do not feel much anxiety on this score. We cannot have many light cases without having a death now and then, and deaths would almost certainly be reported. But what gives me the greatest confidence is that our non-immunes are made up entirely of Spaniards and Americans. The Americans promptly report themselves where there is anything suspicious, for the sake of the better care that they get at Las Animas. The Spaniards are all matriculated at one of the three “quintas,” and go there as soon as they are sick from any cause. These “quintas” are all very anxious to try and catch up to the record of Las Animas, and report every case that they think, by any possibility, will pass the Board. And then, too, I can control the “quintas” by frequent inspections. So it seems to me that there is very little probability of cases being concealed to any extent. Still, we can speak more definitely on this subject about the 1st of December than we can now. All well. With kindest regards, I remain, Very sincerely yours, W. C. GORGAS, Maj. & Surg., U. S. A. Chief Sanitary Officer. To Maj. Walter Reed, Washington, D. C. (6) Army Med. Museum, June 27, 1901. MY DEAR GORGAS: