THE ETIOLOGY OF MALARIAL DISEASES. 431 



the insects in the room where they were liberated, and to the experiment 

 not having been continued long enough. They cite Calandruecio as 

 having observed the degeneration of malarial parasites in the stomach 

 of mosquitoes (species not stated). 



November 13th, 1897, MacCallum, in Baltimore, foiiDcl 

 that the "flagella" of Halteridium and of 

 sesti vo-autumnal parasites constitute the male 

 element, and serve to impregnate the "pig- 

 mented spheres" or female element. In the case 

 of Halteridium the impregnated spheres became con- 

 verted into !notile " vermicules." This transforma- 

 tion was, however, not observed in the human parasites. 



December 18th, 1897, Ross fed mosquitoes upon human 

 blood containing crescentic parasites. The ex- 

 periments were made at Secunderabad, and were 

 reported upon at the time as follows : 



After examining hundreds of mosquitoes fed on 

 malarial blood, always with negative results, he obtained a 

 few which belonged to a species with spotted wings, which 

 he had hitherto not used. As Ross distinctly describes 

 the egg of this species, there is no donbt whatever 

 but that he was dealing with a species of Ano- 

 pheles. The insects were bred from larvae, and fed 

 with blood containing crescentic parasites. Four to five 

 days later peculiar pigmented cells were observed lying 

 within the walls of their stomachs. These cells were 

 round or oval ; the}" measured 12 — 16 fi on the fourth, and 

 20 fi on the fifth day after feeding, and the pigment they 

 contained was similar to that within the malarial para- 

 sites in the blood upon which the insects had been fed. 

 Such bodies could not be found in control mosquitoes. 

 Ross concluded that he had found the mosquito 

 which served as a host for the parasite. 



February 26th, 1898, Ross refers again to his experiments 

 with crescentic parasites. After examining some 

 scores of " dapple-winged " mosquitoes unfed or fed 

 with healthy blood, all the results were negative until 



