RELATION OF ARTHROPODS TO PATHOLOGY—-MAROTEL. als 
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grass, and there lays thousands of eggs for a month, when she dies. 
At the end of four to six weeks these eggs produce little hexapod 
larve about as large as the point of a pin, which as soon as possible 
pass to the body of a vertebrate of small size (reptiles, birds, or small 
mammals, such as moles, mice, or rats). There they grow and are 
transformed into eight-footed nymphs; then into adult males, or 
females, which mate together. From this time the fertile females 
leave their first host, fall on the ground again, climb the shrubbery, 
and from thence attach themselves to the first large animal that comes 
within reach. They then make their way into the hair and fix them- 
selves in place by implanting their beak in the skin. 
In tracing this course of development we return again to the stage 
of the female fixed and immovable; that is to say, to our starting 
point. Of this summary, let us remember two things which we shall 
need to recall a little later, namely: 
First. The adult females alone are parasites of man or the domestic 
animals; the males, nymphs, and larve remain ordinarily on the 
small wild vertebrates, and only occasionally pass to the bodies of 
our large mammals. When they do so, it is simply to move about, 
and never to fix themselves or to suck blood. 
Second. These females have during their whole life only a single 
large mammalian host, and never two, as when they detach them- 
selves from this host and drop to the ground it is to lay eggs and 
die, and not to pass to a second host. They do not go from one to 
another, and can not, therefore, be carriers of virus in the manner of 
biting flies. 
But it is necessary to say at once that all kinds of ticks do not 
develop exactly in this manner. ‘There are some which in the nymph 
stage are parasites of a domestic animal. At the moment of becoming 
nymphs they leave their first host to secure a second, so that the 
species of this group have among the large mammals two successive 
hosts, one for the nymph and one for the adult. Others are parasites 
of domestic animals in the larval stage. They have, therefore, three 
successive hosts, one for the larva, one for the nymph, and a third for 
the adult. 
It is established, in consequence, that from the point of view of 
their parasitism as regards man or the domestic animals the different 
species of the Ixodide group themselves in three catagories, accord- 
ing as they seek one, two, or three hosts. As we shall see in a moment, 
it is a biological fact of the first importance in that which concerns 
the explanation of the pathogenic role of the ticks. 
This zoological preface being finished, it is necessary now to go 
to the foundation of the subject, which comprises two parts. In the 
one, we shall indicate the facts. In enumerating the inoculated dis- 
