116 INSECTS AND MAN 



as the transmitter of a tropical and semi-tropical disease 

 known as filariasis. The disease, which in one form also 

 goes by the name of elephantiasis and Barbados leg, is of 

 a distressing nature, and manifests itself in enormous swel- 

 ling of the afflicted organs ; its cause is a worm which 

 occurs in the blood and lymphatics. 



So long ago as 1863, Demarquay had discovered the 

 immature forms of the parasitic worm, and later, Bancroft 

 brought to light the mature form, which was known as 

 Filaria bancrofti. The discovery of the transference of 

 these blood parasites from man to man by the aid of 

 mosquitoes, in itself of the greatest importance, became 

 doubly important, because it paved the way to similar 

 discoveries with regard to malaria and yellow fever. 



The discoverer, Sir Patrick Manson, described his work 

 at a meeting of the Authors' Club, in 1909, in the following 

 words: "Let me go back to my early years of tropical 

 experience. I was then in the island of Formosa. I took 

 a great interest in the diseases of the people. One disease 

 had a special fascination for me elephantiasis. I puzzled 

 over what might be the cause of this disease, but without 

 finding a satisfactory solution. Later I went to Amoy, 

 a large town on the coast of China, where I saw many 

 more cases and many more forms of the same disease. 

 Still I failed to find an explanation. 



"In 1874 I came to London, and there for the first time 

 I heard that Timothy Lewis, who had done so much in the 

 study of tropical diseases, had discovered that in the blood 

 of a proportion of the inhabitants in certain districts of 

 India there was to be found an organism which he called 

 Filaria sanguinis hominis. This is a microscopic 

 animalcule, eel-shaped, and enclosed in a loose sac, or 

 sheath, within which it wriggles about in the blood very 

 actively. It is sometimes present in enormous numbers 

 hundreds in every drop of blood. These parasites Lewis 

 had found in more than one instance in association with 



