390 RESEARCH IN PROTOZOOLOGY 



still less practicable to make leucocyte counts, althoug-h their ratio 

 to the number of red blood cells and dififerential counts are easily 

 obtained. Since most birds show no symptoms of illness until they 

 are really very sick it is impossible to tell much as to the effect of 

 any treatment by direct observation of the bird itself. 



1 8. Quinine and plasmochin. At the present time there are only 

 two known drugs which have been shown to exert any effect on 

 the bird malarias. One of these is quinine and the other is plas- 

 mochin. When the former is administered in doses of about one 

 and one-half milligrams per day it will always prolong the pre- 

 patent period, and will very often entirely prevent the appearance 

 of parasites, although such birds continue to carry a chronic in- 

 fection thereafter just as if they had recovered normally. Since 

 the M.L.D. for quinine is about six milligrams for a bird of aver- 

 age weight (canaries vary in weight from twelve to nineteen or 

 twenty grams, with a mode of about sixteen and one-half grams) 

 it is not practicable to increase the dose very much, the more 

 especially since the drug has a cumulative effect. Plasmochin is a 

 vastly more effective drug than quinine, as far as bird malaria is 

 concerned. It is also much more toxic, but its therapeutic power 

 is so much greater that the doses required are relatively less toxic. 

 The M.L.D. is about one and one-half milligrams for a bird of 

 average weight, but o.i milligram administered daily for four or 

 five days is enough to entirely prevent the appearance of parasites 

 (although the blood of such birds remains infective, just as with 

 quinine). Roehl (1926) found that doses as small as 0.02 of a 

 milligram were eff'ective when given daily. The value of these two 

 drugs has been discussed in some detail in order to make it clear 

 as to what may be expected of a really effective therapeutic 

 agent. 



PROBLEMS FOR FURTHER INVESTIGATION 



I. Drug therapy. Although much work has been done on 

 malaria, both in birds and man, there is great need for further 

 research, not alone to discover new facts, but to verify experi- 

 mentally certain beliefs which have long been held without any 

 very definite evidence in their favor. The results already obtained 

 with plasmochin show clearly the practical value of research in the 

 field of drug therapy, and we need especially to know exactly how 

 such drugs exert their beneficial effects. Do they act directly on 



