1112 



PATHOGENIC PROTOZOA 



blocks in the center. The merozoites vary in number from eight 

 to twenty-five. In addition to the small and large rings the per- 

 ipheral blood shows, after the fever has lasted sufficiently long, the 

 sexual forms or gametocytes. The infected erythrocyte is never 

 stippled nor swollen, but, on the contrary, may appear shrunken. 

 Both the micro- and macrogametocytes in aestivo-autumnal fever are 

 crescentic in shape, their length being about one and one-half and 

 the width about one-half that of an erythrocyte; the pigment is 

 collected toward the center, which is rather paler in stained speci- 

 mens than the poles. At first sight the gametocytes appear to lie 

 free in the plasma, yet in stained specimens a rim or rib of the pale 



red cell may be seen on the con- 

 cave side. When liberated from 

 the erythrocyte the gametocyte 

 becomes first spindle-shaped and 

 finally oval or round. The male 

 crescent is short and broad, and 

 the female relatively long and 

 slender. 



The Finer Structure of the Plas- 

 modia. The finer details, which 

 are only hinted at in fresh speci- 

 mens and in those stained with Man- 

 son 's stain, can be studied to ad- 

 vantage in those stained with some 

 one of the many modifications of 

 the Romanowski stain, such as that 

 of Wright, Hastings, MacNeal or Giemsa. 



The tertian parasite, which lies in a red cell, may be seen to be 

 divided into a blue cytoplasm and a brilliant red nucleus, and it 

 would be well for the novice to remember that these three conditions 

 must be satisfied before the diagnosis of malaria can be made ; the 

 principal stumbling-block is the blood platelet, often found overlying 

 a red cell, but it, although possessing a ragged blue cytoplasm, has 

 always a relatively large purple nucleus. The chromatin of the 

 young rings is usually present as a single dot, but two such dots 

 are frequently seen. In older forms of the tertian and quartan 

 parasites the various changes found in mitosis may be followed in 

 nucleus. The whole schizogenous cycle may be followed by 



FIG. 159. PLASMODIUM FALCIPARUM. 

 (X1500.) (Army Med. School Col- 

 lection, Washington, D. C.) 



the 



taking blood smears from a single case of malaria at intervals of 



