In February 1901, Dr. H. E. Durham published an abstract of an _interim_ report of the Liverpool School Yellow Fever Commission. He and Dr. Walter Myers, the two Commissioners, had both of them been attacked by the disease, and Dr. Myers had died of it. The report gives evidence that the disease is due to a bacillus which is not the _bacillus icteroides_; and it does not wholly favour the earlier report (1900) of the American Commission. A later Commission to New Orleans, September 1901 to January 1902, reported an extensive series of investigations, which seem rather to support the belief that the _bacillus icteroides_ is the cause of the disease. Later still, this belief is again denied; and, as in rabies, so in yellow fever, the good work has gone on without waiting for the identity of this or that micro-organism. * * * * * Immunisation, by the direct use of an infected mosquito, may be compared with the old custom of inoculation against smallpox. The use of Sanarelli's serum-treatment has not gone far. There remains for consideration the method of keeping down infection by keeping down _Culex_. Three reports, in 1901-1902, come from Dr. Guitéras (Havana), Surgeon-Major Gorgas, chief sanitary officer (Havana), and the Commission at New Orleans. Dr. Guitéras reports that 6 cases of yellow fever (inoculation) were treated in a large "mosquito-proof" building, which also contained cases of other diseases. No prophylaxis was enforced, save the exclusion of mosquitoes; non-immunes visited the yellow fever cases, non-immunes nursed them, and most of the attendants and labourers about the place were non-immunes; but not a single case of infection occurred. The New Orleans Commission reports that, of 200 cisterns, &c., examined in the city for the presence of larvæ, the larva of _Culex_ (_Stegomyia_) predominated in more than 60 per cent. The report of Surgeon-Major Gorgas is very pleasant reading. For two centuries, Cuba had been cursed with yellow fever; then, after the war with Spain, America took it over:-- "The army took charge of the health department of Havana, when deaths (from all causes) were occurring at the rate of 21,252 per year. It gives it up, with deaths occurring at the rate of 5720 per year. It took charge, with smallpox endemic for years. It gives it up, with not a case having occurred in the city for over eighteen months. It took charge, with yellow fever endemic for two centuries--the relentless foe of every foreigner who came within Havana's borders, which he could not escape, and from whose attack he well knew every fourth man must die. The army has stamped out this disease in its greatest stronghold."