5. _Rate of Injection._—Operators should pay particular attention to the rate of administration since it is believed that rapidity of injection accounts for more unfavorable results in the use of arsphenamine than any other one thing. In no case should the rate exceed 0.1 gm. of drug (30 cc. of solution) in two minutes, _i.e._, twelve minutes for the average dose of 0.6 gm. CHAPTER V YELLOW FEVER DEFINITION AND SYNONYMS =Definition.=—Yellow fever is an important epidemic disease of the West Coast of Africa and tropical America caused by a spirochaetal organism, _Leptospira icteroides_. The spirochaete is contained in the peripheral blood only during the first three days of the disease. A mosquito, _Stegomyia calopus_ (_Aedes calopus_), biting a patient during this period of his illness, takes in the organism which undergoes some developmental cycle of the nature of which we are ignorant, but we do know experimentally that a minimum period of twelve days is requisite for the completion of the cycle which makes the mosquito infectious for man. When a susceptible individual is bitten by an infected mosquito there develops, after a period of incubation of from two to five days, a rapid rise of fever, with markedly congested face and severe pains of back and head. About the end of the third day the sthenic manifestations are succeeded by asthenic ones in which jaundice, haemorrhages, particularly black vomit, and anuria are the important features. Faget’s sign of a lack of accordance between pulse and temperature is of great diagnostic importance. =Synonyms.=—Febris Flava, Typhus Icteroides. Spanish: Fiebre Amarilla, German: Gelbfieber, French: Fièvre Jaune. History and Geographical Distribution