216 THE PATHOGENIC FLAGELLATES 



one species of trypanosoma with many varieties, or seventy different 

 ones, cannot be determined on the basis of physiological effects alone, 

 or by the nature of the habitat. 



The uncertainties and the many contradictions which characterize 

 our present knowledge of the parasitic flagellates make the group very 

 difficult to handle from a zoological point of view, and deductions and 

 generalizations made upon the strength of slender lines of evidence are 

 not only premature but very confusing to those who are seriously 

 concerned with protozoology, and distracting to medical men whose 

 energies are directed toward the cure and extinction of diseases due to 

 these organisms. The attempt to classify hemosporidia and flagellates 

 in one group, as certain recent writers have done (Hartmann, Sambon, 

 etc.), rests upon a very shaky foundation of fact, and until that founda- 

 tion is better built, we would do much better to adhere to the older 

 system, which, even if not entirely accurate, at least has the advantage 

 of established familiarity and of accepted limits, while those forms in 

 which the life history is now known can be safely placed. To illus- 

 trate, the Donovan-Leishman bodies were first seen as intracellular 

 parasites, and were classified as aberrant forms of hemosporidia similar 

 to babesia. But with the discovery of the flagellated phase in culture 

 and in the definitive host cimex, the enigmatical " bodies" were found 

 to be only intracellular phases of a flagellated protozoon similar to 

 herpetomonas, and, under the name Herpetomonas (Leish mania) 

 donovani (Mesnil), are today classified as flagellates. Similarly the 

 hematozoic parasite of the little owl, halteridium, was found to be a 

 phase of the life cycle of Trypanosoma noduce, and should be removed 

 from the hemosporidia and placed with the flagellates. 



These two instances, while safely established, do not justify a zoolo- 

 gist or a medical man in jumping to the conclusion that all hemo- 

 sporidia have a flagellate stage, and should, therefore, be classed with 

 the mastigophora (Hartmann), or that all trypanosomes have an intra- 

 cellular stage, or that the hemosporidia, as a group, should be aban- 

 doned (Hartmann). An intracellular stage of herpetomonas or of 

 trypanosoma does not make a sporozoon of either one; nor does a 

 flagellated stage of Plasmodium vivax (if such a stage exists, which 

 is extremely doubtful) or of proteosoma, make flagellates of these 

 any more than the tailed tadpole makes a fish of a frog. The old 

 group hemosporidia should not be given up until each species it now 

 contains is proved to be only a phase of some flagellate. To give it up, 

 or to classify these protozoa under the caption of "blood-dwelling 

 forms" (Sambon, Manson), save for purely physiological or thera- 

 peutic reasons, is misleading and unnecessary. 



With these parasitic flagellates the condition of affairs at present 

 is analogous to that in the group hydrozoa among celenterates. 

 Here many species are characterized by two distinct phases : one, the 



