Insects and Disease 6 1 7 



cared for in the isolation hospital, which is now closed. The benefits of the 

 war waged on the mosquito at Rio Janeiro have been as great as those obtained 

 at Havana, where the vigorous work of the American authorities during our 

 occupation of the islands practically stamped out yellow fever in a city long 

 notorious the world over as a ])lague-center. 



Mosquitoes and malaria. — First of these known cases of the dissemina- 

 tion of human disease by insects to be worked out in detail was the relation 

 of mosquitoes to the breeding and distribution of the causative germs of 

 malaria. Malarial fevers occur the world over and have long been a.ssociatcd 

 in the popular mind with low wet localities or with localities near marsh 

 or swamp. Mosquitoes live in great abundance precisely in such regions, 

 but for a long time no association between mosquitoes and malaria was 

 even suspected. Miasma, the effluvia from low wet ground, was held to be 

 the causative, or at least carrying, agent of malaria. It was not until 1880, 

 when Laveran discovered and described the actual parasitic sporozoon 

 (minute one-celled amocba-likc animal) of malaria, that the actual cause of the 

 disease was recognized. 



Malaria as we know it in the United States is a wide-spread and serious 

 disease, but not commonly a fatal one. But in India five million deaths 

 occurred in a single year, 1897, from malarial fever. Giles declares that the 

 malarial parasite is responsible for by far the greatest proportion of all sick- 

 ness and death in the tropics. "Cholera and plague," he says, "are the 

 insigruficant enemies that perhaps kill a few thousands a year — in an impres- 

 sive way, it is true; but the quiet insidious malaria sweeps off its millions." 

 The serious state of alTairs in India, as well as on the Gold Coast of Africa, 

 on the Roman Campagna, and in other notoriously malaria-stricken regions, 

 finally led to careful scientific study of the life-history of the malaria-pro- 

 ducing sporozoon by well-trained English and Italian physicians and natu- 

 ralists, with the result that we now know in definite and accurate detail the 

 whole marvelous story of the interrelations of the malarial parasite, the 

 mosquito, and the human host. 



Lankester was the first to find an amoeba-like parasite living in the blood 

 of animals, Drepanidium ranarum of frog's blood, but since his discovery 

 numerous other similar protozoon blood -parasites, collectively called Ha;ma- 

 tozoa, have been found in reptiles, birds, bats, cattle, and monkeys. The 

 haematozoon infesting cattle discovered by Theobald Smith, an American 

 investigator, produces the disease known as Te.xas fever, and is spread from 

 animal to animal by ticks. The particular blood-parasites, called Ha;ma- 

 moebae, which produce malarial fevers, are not restricted to man alone, but 

 infest birds, bats, and monkeys as well. 



In 1S85 Golgi discovered that the malaria-producing Hiemamoebae of the 

 human body exist in three varieties, each apparently responsible for one 



