704 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
the biting and sucking arthropods (I insist on these terms) recently 
considered as being simply troublesome, vexatious, uncomfortable, 
and disagreeable, have to be looked upon to-day as capable of becom- 
ing carriers of infection, agents for the propagation and dissemina- 
tion of disease. This is why it will be understood henceforth that 
man and the domestic animals are exposed to certain affections, the 
germs of which are introduced by invertebrate blood-suckers which 
they have previously drawn from the sick vertebrate. 
Such is the method of this new role, which I wish to try to ex- 
plain here and which modern researches have shown to be of more 
consequence, especially in warm countries, than could have been 
suspected previously; so much so that the value of our colonial 
domain is subordinated (the word is not too strong) to the discovery 
of the proper means of neutralizing the pathological action of these 
animals. 
Thus, these arthropods, which ten years ago had only an ordinary 
_and purely zoological interest for us, have assumed prime importance 
both from a medical and a hygienic point of view, and especially in 
tropical countries. The principal forms connected with the latest 
discoveries belong to the order Diptera, or to the family Ixodide. It 
has now been established that they are the sole agents of inoculation 
of seven different maladies, namely, malaria, filariosis, yellow fever, 
trypanosomiasis, plague, piroplasmosis, and spirochaetosis. 
A, PALUDISM, OR MALARIA. 
Commonly called malaria, intermittent fever, swamp fever, or 
simply ‘ fevers,” paludism is, according to unanimous opinion, the 
one human disease which more than any other prevents the acclima- 
tization of Europeans in warm countries. It is due to the invasion 
of the blood by extremely small sporozoans lodged in the red blood 
corpuscles, whence is derived the name of endoglobular heematozoans, 
which it is the custom to give them. They belong to the genus Plas- 
modium and comprise many species, such as Plasmodium malaria, 
the agent of quartan fever; Plasmodium vivax, the agent of tertian 
fever; Plasmodium precow, the agent of irregular, or spring and 
fall fever. 
For a long time it was not known to what these fevers were due. 
Some said that they were due to marshes, whence the name paludism. 
It was also said that they were derived from the air, whence the name 
malaria, which means “bad air.” Finally, it was said that- they 
eame from the soil, whence the name tellurism, which was also 
applied to the disease. 
None of these was correct. All the etiological conceptions were 
wrong, and yet mankind for twenty centuries rested on these false 
