228 DISCOVERY CH. 



destroying the larvae in them. This is not so difficult 

 as it may appear at first sight, because the larvae can 

 easily be distinguished in the puddles and other collec- 

 tions of stagnant water in which they occur. By carrying 

 on a vigorous campaign against mosquitoes, many very 

 malarious places on the earth have been made habitable, 

 and prosperous townships are growing up in districts 

 which formerly sustained only a few sickly and miserable 

 inhabitants. 



Where the teachings of science have been followed, 

 our race has triumphed over its enemies ; where ignor- 

 ance or apathy prevails, the toll is being paid in human 

 lives. This is exemplified not only by malaria, but also 

 by many other diseases which have been studied by 

 scientific methods. During the Spanish- American war 

 the American troops suffered great losses from yellow 

 fever. Inspired by Ross's work, an investigation of 

 the cause of the disease was undertaken, with the result 

 that, like malaria, it was found to be transmitted by a 

 mosquito, though a different kind from that which 

 conveys malaria. 



In the year 1900, the president of the United States 

 appointed a commission of five, with Dr. Walter Reed 

 at its head, to carry out investigations in the Island of 

 Cuba, with the object of discovering the cause of yellow 

 fever. Believing that the mosquito theory could only 

 be tested by actual experiment upon a human subject, 

 one of the members of the commission, Dr. Lazear, 

 permitted himself to be bitten by a mosquito which 

 had previously bitten a person suffering from yellow 

 fever ; with the result that he contracted the disease 

 and died in a few days. He gave up his life for others, 

 and the plain record of his sacrifice upon a tablet erected 

 to his memory reads : " With more than the courage 



