RELATION OF ARTHROPODS TO PATHOLOGY—-MAROTEL. ‘1719 
being produced by ixodids of the first group, which attack only a 
single domestic animal and do not pass from one to another, conse- 
quently being unable to carry the virus. It is, then, alone due to the 
heredity of infection among arachnids that piroplasmosis is trans- 
missible from a sick animal to a healthy one, and this heredity appears 
to us, therefore, as the necessary condition of the propagation of 
infection. 
Piroplasmosis is the best type of hereditary diseases, in the proper 
sense of the word; that is to say, those which are transmissible from 
parents to offspring by means of infection of the eggs, an infection 
sufficiently limited, of course, not to arrest the development of the 
eggs, cause their death, and hence produce a parasitic castration. On 
the contrary, many of the diseases considered as hereditary—tuber- 
culosis and syphilis, for example—are transmissible from mother to 
child only through an accidental lesion of the placenta, permitting 
passive passage of germs. ; 
(c) Finally, a third point in the ixodian theory will detain us, 
namely, Under what form is the parasite transmitted by the ticks? 
Is there a simple inoculation of germs, as by a lancet, in the same 
form in which they have been received by the acarian, or rather is 
there a veritable development of the Plasmodia in the mosquitoes ? 
This question is.still one of those which it is impossible for us to 
answer, because in spite of. the most assiduous efforts it has not yet 
been possible to find the least trace of piroplasms in the body of ticks. 
Quite recently, it is true, the celebrated German microbiologist Koch 
announced that he had seen “ something,” but the description which 
he gives is so vague that really nothing positive can be gathered from 
his communication. 
Simple inoculation, that is, the mechanical transportation of the 
virus is perhaps possible in certain cases, notably for the ticks of the 
second and third groups, which transmit as nymphs, or as adults, the 
germs taken in in the preceding stage, but it is not probable as regards 
the ticks of the first group. Lounsbury, indeed, has shown that adult 
ticks, transferred from a sick dog to a healthy one, never transmit the 
disease. On the other hand, we have seen that the inoculation of 
piroplasms by the progeny of an infected tick is possible only in adult 
age. It is true that this is not altogether general. Theiler, confirmed 
by Laveran and Vallée, showed that bovine piroplasmosis and 
spirochetosis are, in the Transvaal, inoculated by Rhipicephalus 
decoloratus, which are the progeny of infected mothers when they 
reach the larval stage. Further, the limitation of danger to the adult 
females may, as we have already shown, be explained by the fact that 
normally these females alone are parasites of domestic animals. 
Nevertheless, this peculiarity leads one to suppose that there is an 
evolution and permits one to ask whether in the course of its migra- 
