RELATION OF ARTHROPODS TO PATHOLOGY—MAROTEL. ‘TJ11 
Many other trypanosomes are propagated by similar means. 7ry- 
panosoma evansi of “surra” is carried by fleas (Tabanus tropicus 
and 7’. linzola) and by the stomoxes (Stomowis nigra). It is the same 
with 7rypanosoma equinum, which is also carried by fleas and 
stomoxes; with 7’. thedleri, inoculated by the hippoboses (Hippobosca 
rufipes and H. maculata). On the cther hand, “ dourine ” seems to 
evade this rule, for up to the present it is considered as propagated 
entirely by sexual union of the insects. 
EK. PLAGUE. 
Tt is known that the bubonic plague of man is due to a bacterium, 
the Bacillus pestis, and that for some time there was an agreement 
of opinion as to the importance of the role played in the propaga- 
tion of this disease on board ship by the rats. The discussion centered 
around the essential mechanism of this transmission, when in 1898 
appeared the famous theory of Simond, ac- 
cording to which the plague virus was carried 
from the rat to man, not by the rat itself, but 
by the intervention of its fleas (fig. 7). 
Numerous attacks were made on this manner 
of explanation, and the special objection was 
brought forward that the fleas of the rat never 
bit men. This allegation was, however, false. 
Fic. 7.—Head of Pulez irri- 
It has since been recognized that fleas of rats = tans_ of )=man x 30. 
and mice may, from the point of view of their 
relation to man, be classified in two categories. 
Those of the first group do not bite men even 
After Railliet. m. Man- 
dibular lancet; J, lin- 
gual lancet; m’, jaws; 
p, labial palpi; p’, max- 
mee illary palpi. 
after a fast of three or four days. This is 
the case with Pulex fasciatus, Ceratophyllus italicus, and Ctenopsylla 
musculi. But others condescend voluntarily to attack human beings. 
These are Pulex irritans, the ordinary flea of man, which sometimes 
lives on the bodies of ship rats; P. serraticeps, the dog flea, which 
agrees with the preceding; then two other forms peculiar to the rat, 
Pulex pallidus (closely allied to P. irritans) and P. murinus. It is 
established, then, by observations made simultaneously in Italy, 
France, and Australia, that ship rats can harbor at least four species 
of fleas capable of attacking men. 
It remained to ascertain whether these insects were able to carry 
the bacillus of plague. The experiments of Gauthier and Raybaud 
have, since 1902, answered this question in the affirmative, as they 
establish “ that the plague could be inoculated from rats to rats by 
the intervention of their fleas.” The experiment, it is true, has not 
been repeated from man to man, but this is really unnecessary. 
Proust did not hesitate to declare, with all the authority which at- 
45745°—sm 1909——46 
