TRANSMISSION OF DISEASES BY INSECTS 255 



obtain infected blood from a patient during only the first three days of 

 his disease; in other words, the patient is no longer a menace to other 

 persons after three days from the time when he comes down with yellow 

 fever, which is from three to six days after the bite. 



After biting a patient the mosquito cannot convey the infection until 

 at least twelve days have elapsed; thereafter it can transmit the disease 

 for certainly six weeks and possibly eight weeks. 



Dr. James Carroll allowed himself to be bitten by an infected mos- 

 quito and consequently suffered a severe attack of yellow fever. He 

 recovered from this, but was left with an affection of the heart from 

 which he died in 1907. 



Dr. Lazear failed to acquire the disease artificially, early in the 

 course of the experiments; but a little later, while visiting yellow fever 

 patients in a hospital, was bitten by a mosquito which he deliberately 

 allowed to remain on his hand. Five days later he came down with 

 yellow fever, which caused his death. His life was a sacrifice for the 

 benefit of the human race. 



Yellow Fever Mosquito. The mosquito that transmits this fever 

 is Aedes argenteus (Aedes calopus, Stegomyia fasciata) and no other 

 species is as yet known to be concerned in the disease. A . argenteus is 

 limited to warm regions; at a temperature less than 68 F. the eggs do not 

 hatch, and below 62 F. the female does not bite (Reed). The depend- 

 ence of the insect upon warmth for its development explains the 

 cessation of the disease in New Orleans in December, with a mean 

 temperature of 55.3 F. and in cities farther north when frost comes. 

 In Cuba and Brazil the fever has occurred every month in the year. 



Cause of Yellow Fever. The specific cause of yellow fever eluded 

 detection for many years and was regarded by many investigators as 

 being ultra-microscopic. The U. S. Commission produced the disease 

 by the injection of blood serum that had been passed through a bacteria- 

 proof filter. Blood from a subject in whom the disease had been pro- 

 duced by transfusion was capable of infecting a third person. 



The weight of evidence indicated that the unknown cause of yellow 

 fever was an organism rather than a toxin, and in 1919 the organism was 

 discovered by Noguchi to be a spirochaete, which he named Leptospira 

 icteroides. During his investigations in Guayaquil Noguchi succeeded 

 in isolating this spirochaete from the blood of patients and from mos- 

 quitoes as well. He obtained pure cultures of the parasite by inoculat- 

 ing guinea pigs with blood from patients, and was able to produce the 

 disease by inoculation in guinea pigs, dogs and marmosets. 



