SPOROZOA 777 



The various stages may be studied by causing suitable species of 

 anophelines to bite persons with many gametes in their blood, and 

 then dissecting the stomach and observing the changes which take 

 place there. The development is visible in unstained specimens with 

 high, dry lenses. Since there is no essential difference in the develop- 

 ment of the three forms of malaria in the mosquito, they will be con- 

 sidered together. The first stage has already been described in dis- 

 cussing the appearance and behavior of gametes in fresh blood. In 

 the mosquito the process may be followed further; the macrogamete, 

 freed from its enveloping red cell, projects a little mound on its sur- 

 face, and this apparently attracts the microgametes to its neighbor- 

 hood. Into this microphyle one, but never more, of the flagella pene- 

 trates, following which the mound is instantly retracted. The fer- 

 tilized macrogamete, now called a "zygote," soon develops the powei 

 cof vermicular motion, then being called an ookinet, and travels to 

 the wall of the stomach, and, like the coccodia, penetrates an epithelial 

 cell and there encysts, making the oocyst. This grows rapidly and 

 ;soon escapes from its host cell and comes to lie in the outer layers 

 of the stomach wall, and as it grows projects into the body cavity of 

 the mosquito. Tlie nucleus divides repeatedly, always accompanied 

 by some of the cytoplasm, forming numerous sporoblasts, and these, 

 in turn, subdivide into innumerable sporozoites; these last escape, 

 with the rupture of the oocyst, into the body cavity. From there 

 they pass to all parts of the mosquito, but especially, perhaps be- 

 cause of chemotaxis, to the salivary glands and ducts, and when 

 next the mosquito bites a warm-blooded host the sporozoites enter the 

 blood stream and start life anew. 



Cultivation of the Malarial Parasites in Vitro. Bass and Johns in 

 1911 announced the cultivation of a few generations of plasmodium 

 vivax in vitro under strict anaerobic conditions. Ten c.c. or more of 

 blood from a malarial patient is defibrinated and distributed in small 

 test tubes in one c.c. quantities and to it is added one per cent of a 

 fifty per cent solution of glucose. The red cells settle so that they are 

 covered with one-half cm. of serum ; the parasites grow in a thin layer 

 near the top of the cell mass ; beneath this they die, or are phagocyted. 

 The optimum temperature is 19 to 40 C. 



Bass states that he has cultivated all three species of plasmodia 

 by destroying the complement by heating one-quarter to one-half hour 

 at 40 C. Under strict anaerobiasis it was possible to transfer the 

 cultures and to keep them alive for twenty days. 



