PATHOGENIC BACTERIA. 161 



gamete (macrogatnete), a true sexual fertilizing process takes 

 place. In the alimentary canal of the mosquito these fertilized 

 cells penetrate the stomach-walls and form cysts filled with a 

 large number of filiform spores, which are extruded into the 

 body cavity of the insect, and some of which reach the salivary 

 glands, whence they are ejected when the mosquito bites. 

 This cycle of development takes seven or eight days. 

 Differential points of the three forms : 



1. The Tertian Form. The adult forms are large, not very re- 

 fractile, and their outline is somewhat indistinct. There is an 

 abundance of fine pigment-granules, and the ameboid motion 

 is vigorous. Segmenting forms divide into 15 to 20 merozoites ; 

 the sexual forms or gametes are large. The red cell containing 

 the organism is swollen and pale. Sporulation and, therefore, 

 the malarial paroxysm occur every forty-eight hours. 



2. The Quartan Form. The organism is smaller, is more re- 

 fractile, and its outline is more distinct. The pigment is coarse 

 and situated at the periphery of the organism, while the proto- 

 plasmic motion is sluggish. Segmentation forms only 6 to 12 

 spores, and has the regular " daisy-head " appearance ; the 

 gametes are small. The red cells become dark in color, and 

 the cycle requires seventy-two hours. 



3. Estiva-autumnal Form. The adult forms are found mainly 

 in the spleen and other viscera, and do not very often occur in 

 the peripheral blood ; their outline is sharp, and they are highly 

 refractile. The pigment is scanty and fine; the motion is 

 active. A variable number of merozoites is formed usually 6 

 to 12. The gametes are characteristic, being crescentic in 

 shape and very resistant to quinine. The red cell becomes 

 shrivelled and yellowish. The cycle usually takes forty-eight 

 hours, though it is somewhat variable. 



Mixed infections with the different organisms or with two or 

 more broods of the same organism may occur, so that quotidian 

 and irregular paroxysms may be produced. 



Methods of Examination. 



1. Fresh preparations are made by placing a small drop of 

 blood on a slide and a cover-c:lass over it, so that only a thin 

 film is formed. A ring of vaseline is smeared over the edges 

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