8 Guide to Insccis and Ticks 



attached to a drum, which rotates upon its axis liy means of a 

 milled wheel operated by the visitor. Another milled wheel at the 

 side of the instrument enables the visitor to adjust the focus to 

 suit his own e^'esight. The microscope on the West side of the 

 Hall carries twelve slides, that on the East live slides. 



MOSQUITOES AND MALAlilA. 



Malaria is a disease of man caused l)y minute parasites that 

 invade the red corpuscles of the blood. The parasites belong to a 

 very low grade of animals, and are included in the division of the 

 Protozoa known as Hamosporidia. 



Formerly malaria, commonly known in this country as ague, 

 was thought to be contracted by breathing the air of marshy 

 districts, but it is now proved that it is due to these parasites, 

 transmitted from man to man by the bite of certain kinds of 

 mosquitoes or gnats. Although there are many hundreds of 

 species of mosquitoes, it is only those belonging to the genus 

 Anopheles, and only certain species of that genus, that are capable 

 of conveying malarial parasites to man. The parasite multiplies 

 not only in the human blood, but also in the walls of the stomach 

 of the mosquito. 



Various forms of malaria are distinguished by medical men 

 according to the frequency of the recurrence of fever and other 

 symptoms, as tertian, quartan, etc. Each is due to a distinct 

 species of parasite, though the visible differences between the 

 species are very slight. The parasite of pernicious or aestivo- 

 autumnal fever is known under the name of Plasmodium falci- 

 parum Welch ( = Laverania malariae Grassi and Feletti) ; that 

 of tertian fever is Plasmodium vivax Grassi and Feletti, and 

 that of quartan fever, Plasmodium vialariae Laveran. Parasites 

 similar to these frequently occur in the blood of other mammals, 

 more especially in that of apes and monkeys, and also in the 

 blood of birds of many species. 



Malaria is now almost extinct in Northern Europe, but in 

 many parts of the tropics it is still one of the commonest of 

 diseases. At the beginning of the present century, however, 

 practical measures for the extermination of mosquitoes were 

 introduced in many parts of the tropics, and the rigid enforcement 



