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371 
served nuclear multiplication, such as has been described by Wenyon in 
similar forms of Herpetomona’s muscae-domesticae. 
The post-flagellate forms of Leishmania, which are expelled with fche 
faeces, help to keep the species in existence and to spread it; this dispersal 
takes place through the infection per os of other fleas and perhaps also of 
other insects. My experiments, as also those of Archibald (1914), lead me to 
believe that these post-flagellate forms are also capable of infecting, by the 
alimentary tract, dogs and healthy children; this is an example of the con¬ 
taminative mode of infection. 
The description of the developmental cycle of Leishmania in my previous 
notes has been confirmed by Alvarez and Sergent. 
Alvarez described the occurrence of Leishmania , in the pre-flagellate, 
flagellate and post-flagellate stages, in the intestine and faeces of fleas from 
a dog infected experimentally with infantile leishmaniasis; Sergent, in col¬ 
laboration with Lheritier and Lemaire, described Leishmania from the in¬ 
testinal contents and faeces of fleas taken from a dog infected naturally with 
leishmaniasis. The studies of Sergent and his collaborators are highly import¬ 
ant, because these writers, repeating my experiments with infected fleas, also 
succeeded in transmitting leishmaniasis to a healthy dog. 
The study of the developmental cycle of Leishmania in the flea indicates 
the possibility that there may be two methods of infection of the vertebrate 
host; the method of inoculation, by the penetration of the parasite through 
the skin, and the method of contamination, by the post-flagellate forms per os. 
This possibility of a double mode of infection explains not only the wide¬ 
spread distribution of leishmaniasis in dogs, but also the domestic localisation 
of the disease, members of the same family becoming infected by fleas, which 
themselves infect one another by means of the faeces. 
LEISHMANIA, HERPETOMONAS, CRITHIDIA IN FLEAS. 
The morphological study of the Protozoa of herpetomonad and crithidial 
types discovered in fleas reveals characteristics which differentiate them from 
the Leishmania which I have discovered in Ctenocephalus canis and Pulex 
irritans. 
These distinctive characters are most evident in the flagellate stage; in 
this stage the dimensions of Leishmania in fleas, as given above, are very 
different from those of the various species of Herpetomonas and Crithidia 
which have been discovered up to the present in the Pulicidae. 
The Flagellates observed by Sangiorgi in fleas (Pulex serraticeps) attained 
a length of 16-6/x with a breadth varying from 3-6 fx. The flagellum in these 
forms is as long as, or longer than the body; Herpetomonas ctenophthalmi 
described by Mackinnon in Ctenophthalmus agyrtes also attains a length of 22/x, 
without including the flagellum, and a breadth of 2/x (Plate XXII, fig. 1); the 
Herpetomonas discovered by Wenyon in Pulex irritans is about 30 p long, 
