55 



some stages Leishmania presents morphological characteristics almost 

 identical with Herpetomonas. it has been distinguished by the fact that 

 Herpetomonas undergoes its complete developmental cycle (flagellate 

 and non-liagellate) in the intestines of insects, while . Leishmania 

 completes its cycle in two hosts, one a vertebrate and the other 

 an invertebrate. In the vertebrate host it produces a disease with 

 characteristic symptoms — leishmaniasis. 



Leishmania is non-fiagellate in the vertebrate host and flagellate 

 in the invertebrate (Ctenocephalus canis, Pulex irritans). Both 

 forms occur in artificial cultures. Three stages (which may also be 

 noticed in Herpetomonas and Criihidia) are found in the life-cycle of 

 Leishmania in fleas --the pre-flagellate, occurring in the flea's mid-giit, 

 the flagellate in the hincl-gut, and the post-flagellate in the rectum 

 and faeces. 



In Leishmania, as opposed to Herpetomonas and Criihidia, the 

 flagellate form does not seem to be easily found. The post-flagellate 

 forms, expelled with the faeces, help to spread the species through 

 infection per os of other fleas, and perhaps also of other insects. 

 Probably, too, chfldren or dogs might be infected in this way, as well 

 as by inoculation. This would explain not only the widespread 

 distribution of leishmaniasis in dogs, but also the domestic localisation 

 of the disease, members of the same feimily becoming infected by 

 fleas, which themselves infect one another by means of the faeces. 



An accurate study of the complete developmental cycle of the 

 various Herpetomonas and Criihidia already described in fleas reveals 

 certain morphological differences between them and the developmental 

 forms of Leishmania in the same insects ; on the other hand, the 

 morphological study, if it is not supplemented by biological and experi- 

 mental data, may be sometimes insufticient. It is necessary to bear 

 in mind that the herpetomonad and crithidial forms found in fleas 

 are not always insectan flagellates, since developmental stages of 

 trypanosomes {e.g., Trypanosoma lewisi) that possess a herpetomonad 

 or crithidial phase also occur in fleas. 



Experiments and observations of natiu-al disease occurrence 

 [R. A.E., B, i, 130; iv, 102; etc.] show that in mammals, as in reptiles 

 flshes and amphibia (especially in those that are insectivorous), natural 

 herpetomoniases exist, or an infection with an insectan Herpetomonas 

 may be induced, either by wa}' of the chgestive tract or by inoculation. 

 Herpetomoniasis appears to be an infection that is not distinguishable, 

 either by the morphological and biological characteristics of the parasite 

 or by its symptoms, from visceral leishmaniasis. The author conse- 

 quently reaffirms his belief that the leishmaniases are produced by 

 Protozoa {Herpetomonas, and perhaps also Crithidia) that have adapted 

 themselves to live and multiply in vertebrate hosts ; this adaptation 

 is easier in the case of a vertebrate on which the in.sect hosts are 

 ectoparasitic. 



The same species of Herpetomonas of insects, under dift'erent condi- 

 tions, may not have any pathogenic action, or may produce pathogenic 

 eftects in various degrees in different animal hosts. In Mecliterranean 

 leishmaniasis this theory explains the acute forms, the chronic forms, 

 and other spontaneously curable forms that have been distinguished. 

 The disease, and particularly slight cases of it, may be much more 

 frequent than has yet been realised. 



The stud}' of visceral leishmaniasis in the Mediterranean regions, 

 the epidemiological factors of the close relations between leishmaniasis 



