444 ZOOLOGY AND MEDICHsTE. 



the Ixodidse demand the closest attention from physicians. They 

 no longer confine themselves to playing the part of intermittent 

 parasites; they inoculate infectious diseases of incontestable gravity. 

 The scope of our studies enlarges accordingly, and it becomes neces- 

 sary to know, in all its details, in all its metamorphoses, the 

 biological history of these new enemies, within whose bodies the 

 Spirochseta and the Treponema may undergo transformations whose 

 cycle we must also elucidate. 



The Ixodida^, then, have recently revealed themselves to us as the 

 propagators of dangerous diseases. In reality the parasitologists, 

 who must pay attention to comparative medicine or else restrict 

 their view to a quite narrow horizon, already knew of the per- 

 nicious part which these play in the transmission of babesiosis, not- 

 ably in that form known as '' Texas fever.*"' This epizootic decimates 

 the herds of cattle in tlie southern part of the United States, in the 

 Argentine Republic, and even in certain countries of Europe. It has 

 for its cause a ver}^ small, pyriform parasite {Bahesia borls), which 

 lives in the red blood corpuscles whose substance it destroj^s, thus occa- 

 sioning a characteristic hemoglobinuria. The important observa- 

 tions of Theobald Smith and Kilborne showed that this infectious 

 agent was transmitted to the cattle by the Rhipicep/iahts annulatus^ 

 a species of tick of which numerous varieties are widely spread 

 throughout the globe. 



Special kinds of babesiosis occur in the dog, the horse, and other 

 mammals. None has yet been determined in man, at least in an 

 indisputable manner, but it may be reasonably affirmed that this 

 parasitic type probably does not spare our species. Decidedly, while 

 awaiting the study of the Gamasidse and other Acarids, we ought 

 henceforth to give as much attention to the Ixodidpe as to the mos- 

 quitoes, the fleas, the Glossing, and the Tabanida?. Medical zoology, 

 that has already conquered such vast territories in the domain of the 

 protozoa, is now annexing a considerable part of that belonging to 

 the arthropods. 



The studies which we should pursue are therefore as varied and 

 complex as possible. Among the numerous questions that come up 

 with regard to them there is none that is more stimulating at the 

 present time than the mystery that surrounds certain parasites, 

 whose existence is certain and whose animal nature seems very 

 probable, but which we have never yet been able to discover. 



Among this number is the parasite of yellow fever. We know that 

 it is transmitted by a mosquito {Stegomyia calopus), which is not 

 infectious until the twelfth day after it has bitten a person affected 

 with yellow fever — that is to say, until the parasite has undergone, 

 in its organism, transformations which are more of less analogous 



