EXPERIMENTS ON BIRD MALARIA 385 



months after the original attack than either before or after this 

 time, but there is much variation and certain birds are much more 

 prone to relapse than others. Chronic infections with Plasmodium 

 cathcmerium are much less likely to relapse than are those of the 

 other two species. Even though no parasites can be found in the 

 blood of such a case for many months it is no indication that 

 complete recovery has taken place. 



9. Other species. In addition to the three species just described 

 there is a fourth one, according to the Sergent brothers and 

 Catanei (1928), for which they propose the name Plasmodium 

 rouxi. No figures are published in their paper, but it is quite clear 

 from their description that this species of parasite differs from 

 those already discussed both in the type of infection which it 

 causes, and in its morphology. Only four merozoites are produced 

 by each schizont, instead of from twelve to twenty or even more 

 as in the other three species, and the parasites are characterized 

 by the presence of two grains of pigment of unequal size. The 

 infections are always very prolonged, and the prepatent period 

 is said to have an average duration of three weeks. Parasites can 

 be easily demonstrated in the peripheral blood for a very long 

 time, and the death rate is quite high ; of fifty birds infected fifteen 

 succumbed. 



The "Whitmore strain," already referred to, is probably a 

 variety of Plasmodium inconstans. This strain was originally ob- 

 tained by Colonel Whitmore from a New York sparrow in 1913, 

 and has been the subject of considerable work in the United 

 States. It is very probable that there are still other species not yet 

 recognized, for research in bird malaria has not been extensively 

 carried on in the western hemisphere. There are also many species 

 of Hemoproteus, a genus of blood parasites which is without 

 doubt very closely allied to the plasmodia of birds. 



10. Source of parasites for experimental purposes. Malarial 

 parasites for experimental work are generally most easily ob- 

 tained from sparrows, since these birds are usually available almost 

 everywhere and at all seasons of the year. To determine whether 

 a bird is infected a thin smear may be made and examined micro- 

 scopically for parasites, but since very few parasites can usually 

 be found during the latent period of the disease the better way is 

 to inoculate a canary with 200 to 300 cubic millimeters of blood 

 from the suspected bird. If parasites are present in the latter the 



