ZOOLOGY AND MEDICINE. 448 



category. It therefore follows that the assistance or the dipterol- 

 ogist in questions of epidemiology is still more important than we 

 had supposed. 



In addition to the above, it should be said that it is not only nec- 

 essary to establish the nature of pathogenic insects, to ascertain their 

 habits and their metamorphoses, to find the most effective means of 

 destroying them or of driving them away, but also to folloAv in its most 

 minute details the cycle of the evolution of the parasite in the interior 

 of the organs. Yet all this is only one aspect of the matter, and I may 

 say that it is not the most important one. It is, in fact, indispensable 

 to experiment with the parasite itself, so as to arrest, if possible, its 

 invading march, and to determine the conditions capable of attenuat- 

 ing its pathogenic action and of rendering the organism of its host 

 indifi'erent to its attacks. A trypanosoma swarms in the blood of 

 the rat without inconveniencing that animal in any appreciable way. 

 Such an endurance is doubtless the result of a progressive and heredi- 

 tary toleration, which gives reason to suppose that man and the ani- 

 mals that are the present time defenseless as regards the trypa- 

 nosomata are capable also of acquiring immunity. The investigation 

 of the conditions by which this may be established is surely one of 

 the most important problems of the present day. This leads us back 

 to the ever-present topic of phagocytosis and the pathological physi- 

 ology of the white corpuscles. 



But yesterday unknown in human parasitology, the trypanosomata 

 have to-day acquired an important place in this special department of 

 medicine. It may be said that their importance as well as that of 

 the zoological group to which they belong increases every day. 



The Spirocha^ta, assigned for a long time to the bacteria, are really 

 protozoa, in particular flagellata of a somewhat aberrant type. Two 

 diseases of man are caused by them — recurrent fever and the tick 

 fever of central Africa — these having, respectively, as pathogenic 

 ngents the Sph-ochcetuni recui'i'entis and the ^inrochwUmi duttoni. 

 There are also known several kinds of spirochsetosis that affects ani- 

 mals. Now it has been established that these parasitic affections are 

 transmitted by the bite of various kinds of arthropods: Hemiptera, 

 such as the bedbug {Acanthia lectularia) ; and Ixodidse, such as the 

 OrnitJwdorus saingnyi The most redoubtable of the diseases of man, 

 syphilis, of which Schaudinn has recently found the pathogenic agent 

 {Treponema pallidum), is also a kind of spirochsetosis, but it is nor- 

 mally transmitted by the contact of mucous membranes that are 

 ulcerated in a manner that is often inappreciable. In this respect it 

 offers a very striking analogy to dourine or mal de coit which, 

 although due to the existence of a trypanosoma {T. equiperdmn) , is 

 propagated in the same way, without the bite of any insect. 



Apart from these exceptional cases we see why the Hemiptera and 



