136 GENERAL BIOLOGY 



Finally, in August, 1897, seventeen years after the parasite was 

 first discovered in man, he obtained his first clue. 



While he was dissecting a "dappled-winged" mosquito and had 

 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 amongst 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 the mature pigment cells contained 

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

 tured, 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. 

 vSo 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 

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

 a series of popular experiments were tried out. 



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

 went to the most malarial portion of Rome in the most dangerous sea- 

 son. Here 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 mos- 

 quitoes. 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 disease. 



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 experience in cleaning up the Panama Canal Zone of Ma- 

 laria and Yellow Fever are notable examples of preventive measures 

 being 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 para- 

 site 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, and not one developed the 

 disease, while those who were bitten by the infecting mosquito and hav- 

 ing 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. 



