Mosquitoes and Malaria 189 



10. Malarial diseases and likewise mosquitoes are most prevalent 

 toward the latter part of summer and in the autumn. 



1 1 . Various writers have maintained that malaria is arrested by 

 canvas curtains, gauze veils and mosquito nets and have recom- 

 mended the use of mosquito curtains, "through which malaria can 

 seldom or never pass." It can hardly be conceived that these 

 intercept marsh-air but they certainly do protect from mos- 

 quitoes. 



12. Malaria spares no age, but it affects infants much less 

 frequently than adults, because young infants are usually carefully 

 housed and protected from mosquito inoculation. 



Correlated with the miasmatic theory was the belief that some 

 animal or vegetable organism which lived in marshes, produced 

 malaria, and frequent searches were made for it. Salisbury (1862) 

 thought this causative organism to be an alga, of the genus PalmeUa; 

 others attributed it to certain fungi or bacteria. 



In 1880, the French physician, Laveran, working in Algeria, 

 discovered an amoeboid organism in the blood of malarial patients 

 and definitely established the parasitic nature of this disease. Pig- 

 mented granules had been noted by Meckel as long ago as 1847, in 

 the spleen and blood of a patient who had died of malaria, and his 

 observations had been repeatedly verified, but the granules had been 

 regarded as degeneration products, and the fact that they occurred 

 in the body of a foreign organism had been overlooked. 



Soon after the discovery of the parasites in the blood, Gerhardt 

 (1884) succeeded in transferring the disease to healthy individuals 

 by inoculation of malarious blood, and thus proved that it is a true 

 infection. This was verified by numerous experimenters and it 

 was found that inoculation with a very minute quantity of the dis- 

 eased blood would not only produce malaria but the particular type 

 of disease. 



Laveran traced out the life cycle of the malarial parasite as it 

 occurs in man. The details as we now know them and as they are 

 illustrated by the accompanying figure 125, are as follows: 



The infecting organism or sporozoite, is introduced into the cir- 

 culation, penetrates a red blood corpuscle, and forms the amoeboid 

 schizont. This lives at the expense of the corpuscle and as it develops 

 there are deposited in its body scattered black or reddish black 

 particles. These are generally called melanin granules, but are 

 much better referred to as haemozoin, as they are not related to 



