394 RESEARCH IN PROTOZOOLOGY 



24. Whether the changes which take place in the proportions of 

 asexual forms to gametocytes during the course of the disease 

 are due to (a) selective destruction by the host, or (b) 

 whether there is actually a greater production of gametocytes 

 later in the infection. 



25. Whether gametocytes ever develop directly from sporozoites. 



26. Whether, if the proportion of gametocytes developed later 

 in the disease is really greater than that produced earlier, the 

 change is due to the increasing resistance of the host. (This 

 hypothesis might perhaps be tested by making comparisons 

 of the changes in the asexual parasite-gametocyte ratio in 

 birds showing light infections, and in those showing long 

 infections ending in death. For it might be assumed that in 

 the latter case resistance was not increasing in the host as 

 much as in the former.) 



27. The cytology of the parasite, with respect to chromosome 

 number, etc., ought to be investigated, both in the asexual 

 portion of the cycle and in the mosquito. (But this cannot be 

 done successfully until a better method of staining is de- 

 vised.) 



28. Why some mosquitoes afford suitable conditions for the de- 

 velopment of the parasite when others do not. 



29. Whether development, or any part of it, can occur in the 

 body of any other biting insect. 



30. The effect of various environmental agents, such as ultra- 

 violet light, upon the parasite in vitro. (Investigation of such 

 changes should include not only the visible ones, but changes 

 in virulence, etc. And changes in the chromosome number 

 ought to be looked for.) 



31. A practical method of culturing the parasite outside the body 

 of the host. 



32. How pure-line infections (those started from a single para- 

 site) would compare with ordinary ones. 



33. A method of producing pure-line infections. This would not 

 be difficult if cultivation were possible. It might be possible 

 to secure a pure-line infection by infecting a bird with the 

 sporozoites from a single oocyst of an infected mosquito. It 

 is said that as many as 10,000 sporozoites may be developed 

 from such an oocyst, and this would probably suffice for in- 

 fection. 



