EXPERIMENTS ON BIRD MALARIA 391 



the parasite, or is their effect an indirect one due to some inter- 

 action of drug and tissues of the host? 



2. Biology of the parasite. There are still many things which 

 we do not know about the parasite. We need information about 

 its cytology, its life processes, the mechanism and details of 

 gametocyte formation, the question of whether or not a toxin is 

 produced, and the number of species which exist. There are many 

 facts which a careful study of pure-line infections might bring 

 to light, and an entire new field of research would be opened up 

 if wx could cultivate the malarial parasite of birds (or of man) 

 as we do bacteria. 



3. Host-parasite relations. Similarly there are many things 

 ^yhich we do not yet know about the disease in the host, and the 

 reaction of the latter to the parasite. We do not know whether the 

 injury which the latter does the host is confined to the destruction 

 of the red blood cells or not, and, although we have good reasons 

 for supposing that this is not the sole mode of injury, we have 

 little data as to what these other possible modes of injury may be. 



4. Relapse. It is unnecessary to remark that the problem of 

 relapse is one of the most important in the whole field of malaria, 

 and it is likewise a phase of the disease about which we know 

 much less than we ought. We have little information as to the 

 mechanism of the resistance which the host develops towards the 

 parasite, and still less as to why it is that certain mosquitoes make 

 better intermediate hosts than others do. We have as yet no re- 

 liable method for the quick diagnosis of carriers, either avian or 

 human, and we are quite ignorant of just what changes in the 

 host (or in the parasite) may be responsible for the occurrence of 

 relapses. 



5. Geographical distribution. In the case of bird malaria we 

 have not the slightest information as to the geographical distribu- 

 tion of the different species of parasite. W^e know that they are 

 collectively very widespread it is true, but of exact knowledge we 

 have next to none. We also know relatively little as to the par- 

 ticular species of Culex or Stegomyia which act as vectors in dif- 

 ferent regions. 



