The Protozoa 137 



searched every cell and found nothing, he came to the insect's stomach. 

 In writing of this, Major Ross says: "Here, however, just as I was 

 about to abandon the examination, I saw a very delicate circular cell, 

 apparently lying among the ordinary cells of the organ and scarcely 

 distinguishable from them. On looking further, another and another 

 similar object presented itself. I now focused the lens carefully on one 

 of these, and found that it contained a few minute granules of some 

 black substance, exactly like the pigment of the parasite of malaria. I 

 counted altogether twelve of these cells in the insect." 



As he searched further he found that the mature pigment cells 

 contained multitudes of thread-like bodies which, when the parent cell 

 was ruptured, poured into the body of the insect. These were the spores 

 formed in the sexual generation. 



Major Ross did his experimental work on birds which are infected 

 with malaria, but his results were soon found to apply to man as well. 



So complicated a scheme of things can never appeal to men at large, 

 and yet it is just men at large who must assist in any preventive meas- 

 ures which are to wipe out diseases of this nature. For this reason a 

 series of popular experiments was made. 



Drs. Sambon and Low, of the London School of Tropical Medicine, 

 went to the most malarial portion of Rome in the most dangerous season. 

 They lived with three or four others from July until the 19th of October 

 in a specially constructed mosquito-proof hut near Ostia. They were 

 thus protected from sunset to sunrise from the bites of mosquitoes. 

 Not one of them became infected, while mosquitoes sent from here to 

 London were allowed to bite several people (Dr. Manson's own son being 

 one of the subjects who volunteered for the experiment), all of whom 

 came down with the diseases. 



Again, in Italy, railroad employees who were housed in mosquito- 

 proof huts did not develop the disease while those not so housed did. 



Our own experiences in cleaning up the Panama Canal Zone of 

 malaria and yellow fever are notable examples of preventive measures 

 used most effectively, from the knowledge gained in the study of the 

 life-cycle of the malarial parasite. 



In Cuba, yellow fever (also a disease caused by an infecting parasite 

 carried by the mosquito), was shown, likewise, to be carried only 

 through an intermediate host. Major Walter Reed had workmen sleep 

 in beds and use the clothing of those who died of yellow fever, but kept 

 such men housed in mosquito-proof huts. Not one developed the disease, 

 while those who were bitten by the infecting mosquito and having 

 perfectly clean bedding and linen took the disease. Dr. Charles J. Finlay 

 of Havana, Cuba, and Major Walter Reed are the Manson and Ross of 

 the yellow-fever parasite. 



There are 125 species of mosquitoes in North America, but it is 

 only the female of the genus Anopheles which can transmit malaria to 



