Malarial Parasites 



499 



These micro-organisms correspond in all essentials. They are 

 protozoan parasites belonging to the sporozoa and live in the blood 

 (hematozoa) as parasites of the red corpuscles. They all have two 

 life cycles, one which is asexual in the intermediate warm-blooded 

 host, and one that is sexual in the definitive cold-blooded (insect) 

 host. Though the inteirmediate hosts vary and may be birds or 



Fig. 177. — Plasmodium falciparum. Ookinetes in the stomach of Anopheles 



(Grassi). 



mammals, the insect hosts, so far as known, are always mosquitoes. 

 The mosquitoes become infected by biting and sucking the blood of 

 infected animals; the warm-blooded animals become infected by 

 being bitten by infected mosquitoes, and so on, in endless cycles. 



The parasites differ but little in the details of structure and de- 

 velopment, so that the following description may serve as a type 

 for all: 



From the proboscis of the mosquito, with its saliva, from cells in 

 the saUvary glands where they have 

 been harbored, tiny elongate spindles, 

 measuring about 1.5 fi in length and 

 0. 2 ;it in breadth, and tnown as sporozoits, 

 enter the blood of the individual bitten. 

 These sporozoits attach themselves to 

 the red blood-corpuscles, gradually lose 

 their elongate form, and become irreg- 

 ularly spherical. There is some differ- 

 ence of opinion whether the little bodies 

 are simply upon the corpuscles, as Koch 

 believed, or in the corpuscles, as the 

 majority of writers believe, but it is an 

 immaterial difference, for the parasite 

 soon makes clear that it is consuming the 

 Gorpuscle. This little body is known 

 as a schizont. When stained with poly- 

 chrome methylene-blue, and examined under a high power of the 

 microscope, it appears as a little ring with a dark chromatin dot upon 

 one side. It grows steadily, feeding upon the hemoglobin, which 

 seems to be chemically transformed into fine or coarse granules of a 

 bacillary or rounded form, presumably melanin. In a length of 



Fig. 178. — Plasmodium fal- 

 ciparum. Transverse .section 

 of the stomach of Anopheles, 

 showing the ookinetes of the 

 parasite in various stages of 

 development attached to the 

 outer surface (Grassi). 



