714 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
’ 
eases we shall show the magnitude of the réle of the pathogenic ticks. 
In the other we shall seek the explanation of these facts; that is to 
say, the mechanism by the aid of which this réle can be played. 
THE PATHOGENIC ROLE OF THE TICKS. 
It was believed for a long time, and many persons still believe, 
that the ticks are inoffensive parasites. This is an absolute error. 
It has been completely established, indeed, that they are the necessary 
agents in the propagation of many parasitic diseases—for example, 
piroplasmosis, spirochetosis, and ‘“ water-heart.” 
A. Piroplasmosis——The piroplasmoses are contagious affections 
due to an invasion of the blood by sporozoans allied to the plasmodii, 
the species of Péroplasma. Composed of a small mass of protoplasm, 
globular, or pyriform, of from 2 to 4 microns in 
oe diameter, surrounding a minute nucleus (caryo- 
(or. O some), these parasites are inclosed in the red cor- 
Nia (2) puscles, where they are generally grouped by 
@) 
Fie. 8.—Six red cor- 
twos. Sometimes, however, they are single, or, 
on the other hand, united in groups of 4, 8, or 
puscles of an ox af- 
fected by piroplasmo- 
sis. Two corpuscles 
are sound, while the 
16 (ig: SNE 
At present six different species of Piroplasma 
are known: Piroplasma bigeminum, the agent 
of bovine piroplasmosis; P. canis, the agent of 
canine piroplasmosis; P. equi, the agent of 
four others are in- 
vaded by one or two 
round or _ pyroform : ; : 
parasites. Enlarge. equine piroplasmosis; P. parvum, the agent of a 
ment: 000. After special bovine piroplasmosis, called tropical or 
Ligniéres, 
bacilliform (East Coast fever) ; P. donovani, the 
agent of human piroplasmosis (Kala-azar and, according to Mesnil, 
probably also of bouton d’Orient, or tropical ulcer; Biskra carbuncle, 
Aleppo carbuncle, Delhi carbunele, etc.). But this parasite differs 
sufficiently from the other piroplasms to cause certain authors to make 
it the type of another genus, Leishmannia. At all events, all these 
heematozoans are inoculated into their hosts by the punctures of ticks. 
This fact has been more than abundantly proven, especially by 
Smith and Kilborn, and confirmed by Koch and Lignieres, for the 
ordinary bovine piroplasmosis; by Lounsbury for the canine piro- 
plasmosis; by Motas for the ovine piroplasmosis; and by Theiler, 
confirmed by Laveran and Vallée, for the tropical piroplasmosis. 
These experimenters have shown that one can voluntarily produce 
the piroplasmosis by causing healthy animals to be bitten by ticks 
intentionally infected. The species concerned, however. vary accord- 
ing to the piroplasm employed, and also according to the region in 
which it is examined. 
