MALARIA AND THE MALARIAL PARASITE. 315 



body cavity of the insect, being over-distended, ruptured and discharged 

 the rod-like bodies into the body cavity of the mosquito. For a time 

 Ross could get no further than this. He could not find what became 

 of the rod-like bodies. One day, in dissecting the head of a mosquito, 

 he encountered two small trilobed glands the ducts from which united to 

 form a main duct. The glands lay on either side of the head and the 

 common duct he traced to the base of the proboscis of the mosquito. 

 This was the salivary gland of the mosquito. He found that the cells 

 of the gland contained rod-like bodies exactly like those which he had 

 found inside the parasitic capsules in the stomach-wall. He concluded 

 that somehow these 'germinal rods' (for so he called them) had managed 

 to find their way into the salivary gland of the mosquito. It imme- 

 diately occurred to him that this might be the route by which the para- 

 site escaped from the mosquito into its vertebrate host. No sooner 

 had the idea occurred to Eoss than he put it to the test of experiment. 

 He selected a number of sparrows in whose blood he satisfied himself 

 that there were no parasites and let loose upon them a number of 

 mosquitoes which he had already infected with malarial parasites. He 

 found after a week or ten days that the sparrows which were experi- 

 mented upon sickened and many of them died; and in their blood he 

 found the malarial parasite. 



We now understand why the flagellated body is developed outside 

 the human host: because its function lies outside the human host. We 

 now understand why the flagella break away and enter the granular 

 sphere: they impregnate it and start it on the road of development. 

 We now understand why MacCallum's vermicule is beaked and endowed 

 with powers of locomotion and penetration: that it may approach and 

 penetrate the stomach of the mosquito. And we now know why the 

 sporozooites, the 'germinal rods,' enter the mosquito's salivary gland: 

 that they may be injected into vertebrate issue and so pass the parasite 

 from vertebrate to vertebrate. 



This is one of those fairy tales of science which people are inclined 

 to doubt, but any one who has worked at the subject and taken the 

 trouble to go through the long series of preparations which have been 

 sent home from India can not for a moment have the slightest doubt 

 that what Ross stated was absolutely true, and that not only for bird 

 but for human malaria. So soon as the idea got abroad that the key 

 to the way in which the malarial parasite is propagated had been found 

 the Italians immediately set to work with renewed vigor and with the 

 utmost skill. Almost at once they demonstrated that what happened 

 in the case of Ross's sparrows happened also with the human subject: 

 that the appropriate species of mosquito fed upon the human malarial 

 subject and subsequently allowed to feed upon a non-malarial subject 

 conveyed the malarial parasite and malarial disease, and that the ap- 



