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120 the Board should themselves be the subject of experiment. Consequently, in the first group of eight inoculations by the bites of mosquitoes hatched from Dr. Fin lay's eggs, administered between i August and 19 August, Dr. Lazear was included as Case No. 6. The result in all eight cases, listed in the report by number only, was negative — no yellow fever. The same thing was true of Case No. 9, that of Dr. A. S. Pinto, bitten on 25 August by a mosquito infected 10 days earlier." 22

But on 27 August, Dr. Carroll was bitten by a mosquito infected 12 days before — and on 31 August, Dr. Carroll sickened with a well-defined and very severe case of yellow fever, the first such case traceable to the bite of an infected mosquito under experimental conditions. Dr. Carroll's case came very near to proving fatal and, in its aftereffects, undoubtedly shortened his life. The second case of experimental yellow fever was that of Pvt. William H. Dean of the Seventh Cavalry who, on 31 August, the day that Dr. Carroll was taken sick, was bitten by the same mosquito which had infected him, and also by three others which 12 days before had fed on the blood of yellow fever patients. Dean, referred to in the original reports of the investigation as "XY," had a mild but definite attack of yellow fever. 23

Up to this time, there had been eleven "bitings" by the experimental mosquitoes, with but two cases of fever resulting — a circumstance which was afterward found to be due to the fact that only the female of the species could transmit the disease, and she could not do so until at least 12 days after becoming herself infected, and that the first nine "bitings" had been too soon after the mosquitoes had been fed on yellow-fever blood. Moreover, there was a shadow of doubt as to whether Major Carroll's case was of experimental or accidental origin, since he had been in infected areas before and after being bitten. As to the case of Private Dean, however, there was no doubt, since he had been a patient in the post hospital at Columbia Barracks, and had not been exposed to any source of infection other than the four experimental mosquitoes.

In addition to the two cases of Carroll and Dean, there was the tragic case of Dr. Lazear, who was stricken on 18 September and died a week later. After his death, a notebook containing entries about his experiments was found in the pocket of a uniform which he had been wearing. This little notebook, when analyzed by Reed, furnished the clue to the secret of mosquito transmis-