YELLOW FEVER AND MOSQUITOES 241 



activities, and soon bore through the stomach wall and 

 enter the tissues. A complicated series of changes then 

 takes place, resulting in the development of an enormous 

 number of spindle-shaped cells, which make their way 

 into the salivary gland of the insect. When a mosquito 

 at this stage bites a human being the parasites escape 

 through the wound into the blood, and once more enter 

 upon their so-called life cycle. 



Yellow Fever and Mosquitoes. — The sudden on- 

 slaught, deadly character of the disease, and the help- 

 lessness of the population of the stricken district to ward 

 off attacks, have made yellow fever one of the most 

 dreaded of human diseases. Efforts. were made in former 

 times to combat the scourge by isolating the patient, 

 fumigating every article sent out and otherwise treating 

 the case as though it were smallpox. But these attempts, 

 entailing a vast amount of labor and expense, proved of 

 no avail. People who had never been near a yellow fever 

 victim were smitten, and the only safe course was to 

 leave the region. 



In the year 1900, while the American troops were 

 in Cuba, a Yellow Fever Commission was appointed to 

 make a thorough investigation of this disease. Acting 

 upon the suggestion of Dr. Finlay of Havana that a 

 certain species of mosquito is the responsible agent in 

 transmitting the disease. Dr. Carroll of the Commission 

 allowed himself to be bitten by a mosquito that previ- 

 ously had fed upon four patients suffering from the fever. 

 In a short time he was stricken and ultimately recovered. 

 One of his co-workers. Dr. Lazear, was accidentally bitten 

 by an infected insect and died. Other men allowed them- 

 selves to be bitten, and five days later developed the 

 characteristic symptoms. After a long series of investi- 

 gations it was proved that (1) yellow fever is transmitted 

 in no other way than by one kind of mosquito; (2) that 

 to transmit the disease the parasites must be devoured 

 by the mosquito during the first three days of the fever; 



