394 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, Vol XX. 



very peculiar crescent shape in the case of Malignant Tertian 

 Malaria ; and circular or oval in shape in the case of Quartan and 

 Tertian Agaie. These forms of the parasite did not undergo 

 subdivision in the blood ; but some of them underwent a peculiar 

 change known as flagellation in blood drawn from the body and 

 kept under certain conditions for a short time. 



As these peculiar forms did not appear to bear any definite 

 relation to symptoms of fever some observers supposed that they 

 were merely degenerating parasites, and some that they represent- 

 ed a resting stage of the organism, but others hazarded the opinion 

 that they were connected with the transmission of the infection, 

 though in what way they could not explain. 



In 1898 Ross who had been experimenting with mosquitoes for 

 a number of years at the suggestion of Sir Patrick Manson, made 

 the momentous discovery that when mosquitoes of a certain 

 species were allowed to bite sufferers from Malaria in whose blood 

 these special forms of the parasite were present, the latter instead 

 of being digested or disappearing, underwent a change and 

 penetrating the stomach wall of the insect became encysted there. 

 Continuing his observations Ross found that these encysted para- 

 sites which took the form of small tumours in the wall of the 

 mosquitoes' stomachs, rapidly grew larger and larger until they 

 were many times the size of the original parasite ; and gradually 

 as they increased in size the character of their contents changed 

 also, until they appeared to be packed with thousands of little 

 spindle-shaped bodies. Following them a stage further Ross 



discovered that after a time the cysts burst and discharged their 



i 

 contents into the body-cavity of the mosquito, and that finally 



many of the little spindle-shaped bodies were carried to the 



salivary or poison gland of the insects. 



In this way one of the most remarkable zoological researches 



was brought to a successful conclusion. For Ross showed that 



the large pigmented parasites which did not undergo division in 



the human body but which when taken into the stomach of an 



anopheles mosquito commenced to develop there, were sexual 



forms of the malarial organism which required to enter a new type 



of host before they could combine and complete their cycle of 



