4 transactions liverpool biological society. 



Malaria. 



As you know, this disease is transmitted by mosquitoes, 

 but only by a certain sub-family, the Anophelinae, and 

 further by only a limited number of these, though why 

 some of these transmit while others do not, we do not know. 

 The mode of transmission is as follows : At a certain stage 

 of the fever the malarial parasites, which up to this time 

 have multiplied in the blood and given rise to the fever, 

 presumably by a toxin they secrete, become specialized into 

 sexual forms male and female. When the blood containing 

 these is sucked in by a mosquito, fertilization occurs in the 

 mosquito's stomach. That this is so, is, I may add, rather 

 hypothetical, as it has not been actually observed, though 

 once or twice only, fertilization has been stated to have been 

 observed under the microscope, in an ordinary wet blood 

 film. One observer, indeed, believes that fertilization takes 

 place in the blood stream, and suggests that this is the explana- 

 tion why it has been observed so rarely on the slide under the 

 microscope, and never actually in blood taken directly from 

 the stomach of a mosquito immediately after it has fed. 

 Whatever be the truth of this, the next stage is one that can 

 readily be seen in a dissected-out stomach, viz., the encysted 

 fertilized parasite — the oocyst. These are eventually found 

 in numbers from one to two up to a hundred or so on the outer 

 surface of the stomach, viz., in the muscle wall. Growth proceeds 

 in these oocysts, and after various changes the now large 

 oocyst is filled with large numbers of thread-like curved bodies 

 about 12-14ya long — the sporozoites. These travel — how has 

 not been followed — to the salivary gland of the mosquito and 

 from there they escape, during the act of biting, into the blood, 

 say, of a healthy person. Their actual escape has not indeed 

 been seen, but we can safely affirm that they do escape, as 

 healthy people bitten by infected anophelines contract malaria. 



