4i8 



SPECIFIC MICRO-ORGANISMS 



amceba prcecox. 1 The parasite is very common in the blood of 

 small birds, such as sparrows, robins and larks, in all parts of the 

 world. The cycle of schizogony is completed in the peripheral 

 circulation. The small merozoit or agamete enters an erythro- 

 cyte and enlarges, retaining its oval or circular form. The nucleus 



FIG. 188. Proteosoma prcecox in the blood of a field lark (Glauda arvensis). 

 A, Young parasite in a blood cell. B, Half-grown parasite which has pushed aside 

 the nucleus of the erythrocyte. C. Parasite with clump of pigment and many nuclei 

 The nucleus of the erythrocyte has been lost (uncommon). D, Divisicn into eighteen 

 merozoits. (From Doflein after Wasielewski.) 



of the host cell is pushed out of position but its form is not ma- 

 terially altered. The full-grown parasite segments, producing 

 i o to 30 merozoits and leaving behind a small residual body con- 

 taining the accumulated pigment, thus completing the asexual 

 cycle, which may be repeated many times. After a time some 



FIG. 189. Midgut of a culex mosquito, covered with oocysts of Proteosoma prcecox 

 V, Vasa malpighii. (From Doflein after Ross.) 



of the growing parasites become differentiated to form macro- 

 gametocytes and microgametocytes, which are kidney-shaped and 

 do not divide nor undergo further development in the vertebrate 

 host. When the blood is drawn and diluted with citrated salt so- 

 lution, or taken in by a mosquito, four to eight microgametes are 



l Centrabl.f. Bakt., 1891, Bd. IX, S. 407. 



