PROTOZOA 203 



active. A variable number of merozoites is formed usually 

 six to twelve. The gametes are characteristic, being cres- 

 centic in shape and very resistant to quinin. The red ceil 

 becomes shriveled 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. 



Transmission. Malaria is spread by means of a mosquito, 

 the anopheles, in whose body the protozoon undergoes its 

 highest development. Man is the intermediate host; the 

 mosquito, the true host. 



Methods of Examination for Malarial Organisms. 

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

 blood on a slide and a cover-glass over it, so that only a thin 

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

 the cover-glass to prevent evaporation. This is the best 

 method for studying flagellation and fertilization, but is less 

 satisfactory for routine clinical work than 



2. Stained Smears. These are made by spreading a drop 

 of blood in a thin film over one slide with the edge of another, 

 drying in the air, and staining. Many stains have been 

 devised for the malarial organism, but Jenner's or Wright's 

 is sufficient for ordinary use: 



(i) Jenner's Stain. This is excellent for routine work, as 

 no preparatory fixation is required. The smears are dropped 

 into this stain for one to three minutes, without previous 

 fixation, and at once rinsed in distilled water. The malarial 

 parasites are stained blue, the cell-bodies a reddish brown. 



Fig. 101. Various forms of malarial parasites (Thayer and Hewet- 

 son): i-io inclusive, tertian organisms; 11-17 inclusive, quartan organ- 

 isms; 18-27 inclusive, estivo-autumnal organisms. 



i, Young hyaline form; 2, hyaline form with beginning pigmenta- 

 tion; 3, pigmented form; 4, full-grown pigmented form; 5, 6, 7, 8, seg- 

 menting forms; 9, mature pigmented form; 10, flagellate form. 



n, Young hyaline form; 12, 13, pigmented forms; 14, fully devel- 

 oped form; 15, 16, segmenting forms; 17. flagellate form. 



1 8, 19, 20, Ring-like and cross-like hyaline forms; 21, 22, pigmented 

 forms; 23, 24, segmenting forms; 25, 26, 27, crescents. 



