RELATION OF ARTHROPODS TO PATHOLOGY—MAROTEL. leg 
some biologists, at whose head is an indefatigable practitioner, Még-. 
nin, who, to the time of his death, remained one of the most ardent 
and persevering adversaries of the ixodid theory. It is necessary to 
confess that this hesitation is comprehensible, because a goodly part 
of the history of the intimate mechanism of this transmission still 
escapes us, while another part is very strange. 
However, here are some of the peculiarities which are observed : 
(a) The study of the evolution of ticks has shown us that in species 
having a single large mammalian host the adult female alone sucks 
blood. Consequently, they alone can inoculate the parasites which 
this fluid contains. The males, nymphs, and larve remain ordinarily 
on small wild animals. At all events they never bite men nor domes- 
tic animals. They are, therefore, inoffensive, and the females alone 
are dangerous. That the noxiousness is confined to one sex is the first 
peculiarity; the second is as follows: 
(6) A priori, the role of a carrier of virus seems to necessitate 
for ticks, as for insects, successive transfers from one host to another. 
Thus it can easily include the species of groups 2 and 3, which, in 
turn, are transferred to two or three hosts. One can conceive, for ex- 
ample, that equine piroplasmosis may be carried by hipicephalus 
evertst, which has two successive hosts, and which, consequently, may 
be infected as a nymph and inoculate as an adult. Thus, also, 
Piroplasma parvum may be inoculated by Rhipicephalus appendicu- 
latus and R. simus, which have three successive hosts, and may be 
infected as larve, or nymphs, and in consequence transmit the 
infection in the succeeding stage; that is, when nymph or when adult. 
But for the species of the first group, which during their whole life 
have only a single large-mammal host, and consequently never pass 
from one to another, the role of necessary carrier which is attributed 
to them is in direct contradiction to their habits. However, this 
role is an incontestable reality, but it. is carried out by an indirect 
process of a most singular nature. It is known to-day, owing to ex- 
perimentation, that the young female ticks of an infected mother are 
themselves infected, and that they can inoculate their parasites when, 
having become adult, they in their turn, like their mother, pierce the 
skin of an animal. The proof is furnished from different quarters 
so far as piroplasmosis is concerned. For example, Lounsbury writes 
that the progeny of adult ticks (Temaphysalis leachi) fed on sick 
dogs can transmit the disease when they become of adult age, but at 
this age only. In the larval and nymph stages they are absolutely 
innocuous. The same has been established for bovine piroplasmosis 
by Smith and Kilborne and for ovine piroplasmosis by Motas. 
It results, therefore, from these researches that the ixodids of the 
first group can only transmit the germs of disease by the interven- 
tion of their descendants when the latter arrive at adult age. These 
