TRANSMISSION OF DISEASES BY INSECTS 237 



In a later experiment on the island of Formosa, one company of 

 Japanese soldiers was protected from mosquitoes and suffered no malaria, 

 while a second and unprotected company contracted the disease. 



The evident preventive measures to be taken against malaria are 

 (i) the avoidance of mosquito bites, by means of screens and washes of 

 eucalyptus oil, camphor, oil of pennyroyal, oil of tar, etc., applied to 

 exposed parts of the body; (2) the isolation of malarial patients from 

 mosquitoes, in order to prevent infection; (3) the destruction of mosqui- 

 toes in their breeding places, especially by the use of kerosene and by 

 drainage. During unavoidable exposure in malarious regions, quinine 

 should be-taken in doses of six to ten grains during the day at intervals of 

 four or five days (Sternberg). 



Culex and Anopheles. The mosquitoes of North America number 

 one hundred and twenty-five known species. Of these only the genus 

 Anopheles transmits malaria to man, though in India, Ross found that 

 Culex transmits a form of malaria to sparrows. These two common 

 genera are easily distinguishable. In Culex the wings are clear; in 

 Anopheles they are spotted with brown. In Culex when resting, the axis 

 of the body forms a curved line, the insect presenting a hump-backed 

 appearance; in Anopheles the axis forms a straight line. Culex has short 

 maxillary palpi, while in Anopheles they are almost as long as the probos- 

 cis. The note of the female Anopheles is several tones lower than that of 

 Culex, and only the female is bloodthirsty, by the way. As regards eggs, 

 larvae and pupae, the two genera differ greatly. The eggs of Culex are 

 laid in a mass and those of Anopheles singly; the larvae of Culex hang 

 from the surface film of a pool. at an angle of about forty-five degrees, 

 while those of A nopheles are almost parallel with the surface of the water 

 in which they live. 



The bite of an Anopheles is not necessarily injurious, of course, unless 

 the insect has had recent access to a malarious person. Anopheles may 

 be present where there is no malaria. On the other hand, it has been 

 found impossible to prove that malaria exists where there are no A noph- 

 eles mosquitoes. Finally, fevers are sometimes diagnosed as malarial 

 which are not so. 



Possibly the malarial parasite can complete its cycle of development 

 in othei animals than man. It is also possible that originally the mala- 

 rial organism was derived by mosquitoes from the stems or other parts of 

 aquatic plants, and that its effects on man are incidental phenomena. 



