3. The patient is a source of infection only during the first three or four days of the disease (this after the three to six days of incubation). 4. The virus must undergo an incubation period of twelve to fourteen days in the mosquito before she is capable of transmitting the disease. 5. The parasite, whatever it is, has never been seen. It is probably too small to be seen by any of our present microscopes, even the recently invented ultramicroscope. It is probably not a bacterial parasite but very likely a Protozoan, and certain specialists have even shown by the study of all the available data that it almost certainly belongs to the Sporozoan genus _Spirocheta_. Now what does all this mean? It means the saving of hundreds of human lives annually. It means the banishing from many localities and possibly very soon from the face of the earth of a disease that since the earliest settlements on this continent has been a source of terror. It means the making habitable of certain places which heretofore a white man has entered only at the risk of his life. It means that quarantines need no longer be established when yellow fever breaks out in a district; quarantines which have inevitably caused the loss of millions of dollars to the world of commerce. RESULTS IN HAVANA The first practical work based on these findings was done in Havana. The Yellow Fever Commission made their recommendations in 1900. In 1901 and 1902 they were put into effect. The following table of the death rate there during a period of ten years shows graphically the results: DEATHS IN HAVANA FROM YELLOW FEVER -----+------+------+------+------+------+------+------+------+------+------ | 1893 | 1894 | 1895 | 1896 | 1897 | 1898 | 1899 | 1900 | 1901 | 1902 -----+------+------+------+------+------+------+------+------+------+------ Jan. | 15 | 7 | 15 | 10 | 69 | 7 | 1 | 8 | 7 | 0 Feb. | 6 | 4 | 4 | 7 | 24 | 1 | 0 | 9 | 5 | 0 Mar. | 4 | 2 | 2 | 3 | 30 | 2 | 1 | 4 | 1 | 0 Apr. | 8 | 4 | 6 | 14 | 71 | 1 | 2 | 0 | 0 | 0 May | 23 | 16 | 10 | 27 | 88 | 4 | 0 | 2 | 0 | 0 June | 69 | 31 | 16 | 46 | 174 | 3 | 1 | 8 | 0 | 0 July | 118 | 77 | 88 | 116 | 168 | 16 | 2 | 30 | 1 | 0 Aug. | 100 | 73 | 120 | 262 | 102 | 16 | 13 | 49 | 2 | 0 Sep. | 68 | 76 | 135 | 166 | 56 | 34 | 18 | 52 | 2 | 0 Oct. | 46 | 40 | 102 | 240 | 42 | 26 | 25 | 74 | 0 | 0 Nov. | 28 | 23 | 35 | 244 | 26 | 13 | 18 | 54 | 0 | 0 Dec. | 11 | 29 | 20 | 147 | 8 | 13 | 22 | 20 | 0 | 0 -----+------+------+------+------+------+------+------+------+------+------