Malarial Parasites 



475 



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 intermediate hosts vary and may be birds or 



*i '' SJ'^KSP 



Fig. 178. Plasmodium falciparum. Ookinetes in 



(Grassi). 



the stomach of Anopheles 



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 salivary 

 glands where they have been harbored, 

 tiny elongate spindles, measuring about 

 1.5 M in length and 0.2 ju in breadth, and 

 known as sporozoits, enter the blood of 

 the individual bitten. These sporozoits 

 attach themselves to the red blood-cor- 

 puscles, gradually lose their elongate 

 form, and become irregularly spherical. 

 There is some difference of opinion as 

 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 immate- 

 rial difference, for the parasite soon 

 makes clear that it is consuming the corpuscle. This little body 

 is known as a schizont. When stained with polychrome meth- 

 ylene-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 time that 



Fig. 179. 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). 



