xiii, b. i Barber: The Transmission of Malaria 45 



In summary, the evidence seems clear that these experimental 

 cases were infected with malaria as the result of exposure to A. 

 rossi infected in the laboratory. The possibility of a relapse 

 from a former infection must be always taken into account in 

 such experiments when performed in a malarious country. But 

 that such relapses should follow exposure to infected mosquitoes 

 in two cases, one occurring fourteen and the other seventeen 

 days after exposure, would be a remarkable coincidence indeed, 

 especially in view of the fact that both patients had been known 

 to be free from fever many days before the experiments and 

 that both showed the same type of parasite as that that in- 

 fected the mosquitoes. 



It also seems clear that a single mosquito of A. rossi may infect 

 at one exposure. The fact that the case that received sporo- 

 zoites from two infected mosquitoes, and, presumably, the larger 

 dose, showed an earlier appearance of parasites and the more 

 marked symptoms may be only a coincidence, but it is worthy of 

 note. One can do little more than guess at the number of sporo- 

 zoites injected by a single mosquito, but judging from the number 

 of sporozoites found at dissection after feeding on the experi- 

 mental cases and comparing with the numbers observed in the 

 salivary glands of many infected mosquitoes of the same species, 

 one would say that the effective number is a matter of hundreds 

 rather than of thousands, and more probably a matter of scores. 



It is noteworthy that the case (No. 408) that had the longer 

 incubation period (seventeen days), the fewer parasites, and 

 the less severe symptoms had a marked enlargement of the spleen. 

 No. 727, with the shorter incubation period (fourteen days), the 

 greater number of parasites, and marked symptoms, showed no 

 enlargement of the spleen. This case had a history of a previous 

 attack, while No. 408 had none. It is interesting to compare 

 gamete carrier No. 1997 (Table IX), who showed enormous 

 numbers of subtertian parasites, practically no symptoms, and 

 a marked enlargement of the spleen. He had a history of a 

 previous attack. This small group of three cases certainly serves 

 well to show the great variety of manifestations observable in 

 subtertian malaria. 



ACKNOWLEDGMENTS 



In the work included under both Part I and Part II I am under 

 great obligations to the Government of the Federated Malay 

 States, especially in the matter of transportation and hospital 



