THE PATHOGENIC HEMOSPOBIDIA 287 



cause of bird malaria, are not different in essentials from similar 

 phenomena in human parasitic forms. 



Of great importance in the malaria problem is the fact of latent 

 and recurrent malaria. In many cases, months after the first attack 

 and apparent cure, the victim suffers anew from the parasites, and 

 this without new infection. The matter has been studied carefully by 

 many observers, among others by Craig and by Schaudinn, and it has 

 been found that parasites, even after apparent cure, are stored up in 

 the spleen and the bone marrow, where they live a comparatively pas- 

 sive existence, getting into the peripheral blood when the conditions for 

 their further development are favorable. Wliat these conditions are 

 is the one remaining obscure point in our knowledge of the malaria 

 organisms. Schaudinn claims that certain of the forms of Plasmodium 

 vivax, which under ordinary conditions would form the macrogameto- 



FiG. 113 



A 





Regression and merozoite formation (parthenogenesis) in Plasmodium vivax. (After 

 Schaudinn.) A, macrogametocyte in blood with nucleus differentiating into a denser and a 

 lighter part; B, the denser part of the nucleus now divides preparatory to schizogony, C, D, 

 while the paler portion with a part of the original cell degenerates; D, numerous merozoites 

 formed about the divided nucleus. 



cytes, undergo a process of parthenogenesis (Fig. 113), whereby the 

 vitality is again renewed and with this the ability to withstand the 

 natural or acquired immunity of the host. Craig, on the other hand, 

 describes the conjugation of two schizonts within the human blood 

 cell, an observation which Ewing ('01) and Wright ('01) had also made, 

 although in the last two cases in connection with the normal infection 

 and not with recurrence, while the occurrence was stated as rare and 

 exceptional. Craig ('05 and '07), however, claims that the union of 

 schizonts is a normal process in every infection, and sees in this fact a 

 means by which the organisms renew their vitality aiul thus bring 

 about recurrence. Minchin doubts the interpretation of this fusion as 

 given by Wright and by Ewing, and regards it as a process of plasto- 

 gamy without sexual significance. Craig's view is certainly enticing, 

 but we must not forgot that jilastogamy is a very common phenom- 

 enon throughout thn group of protozoa and occurs frequently when 



