718  . ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
parasites can only be inoculated by the young female ticks of those 
which are infected, and the propagation of piroplasmosis affords the 
particular information that the piroplasm passes from invertebrates 
to vertebrates, not by the invertebrate itself, but by its progeny. 
In order to understand this it is necessary to admit that the dis- 
ease germs gathered by the young acarian progeny of an infected 
mother have been transmitted to them by their parents, which is 
equivalent to saying that among ticks piroplasmosis is hereditary. 
This, then, is the peculiarity in the mode of action of ticks, that the 
transmission of the parasites is effected not by the acarians which 
have sucked blood, but by their descendants as the result of heredity. 
How is this heredity produced? This is a question which science has 
not yet answered. 
One may believe, however, a priori, that it is due to the fact that 
the infection of the body of the tick by the piroplasms affect, among 
other organs, the ovary and in consequence the embryos. In return 
the eggs derived from these ovules are themselves parasitized, as the 
infection may then be transmitted from the egg to the larva, from 
the larva to the nymph, and finally from nymph to adult. 
If this supposition be correct, all the individuals born of an infected 
mother should be infected, but as among these individuals the adult 
females alone bite domestic animals it results that they alone are 
dangerous. This is a fact which we have already noted, and which 
here finds its explanation. The hypothesis of an infection of the 
eggs received valid support from the observations made by Siegel in 
1903 on an hematozoan allied to the piroplasms—//emagregarina 
stepanovt. It lives in the blood of the marsh tortoise, and its imme- 
diate host is a leech, Zementaria costata; for Siegel found the germs 
of this parasite in the esophageal glands and in the embryoes of the 
leeches, which proves that there was an infection of the egg. 
Similar facts were pointed out by Schaudinn in the same year, as 
regards the hemogregarine of the lizard, but they are more con- 
vineing, because this time the intermediate hosts, as far as observed, 
are not only leeches, but ixodids like the piroplasms. The strong 
light thrown on the subject by these discoveries clearly permits us to 
suppose that for the piroplasms, as for the hemogregarines, heredity 
is due to an infection of the egg. 
The question may be asked, Is it the same for the spirochets? No 
one knows at present, but at all events it is indicated by the researches. 
Already in 1905 Borrel and Marchoux showed that spirochetosis of 
Brazilian fowl indicated a generalized infection of the tick by the 
spirochet, and that this infection involved especially the ovary, so 
that it is probably hereditary, like all the piroplasmoses. However 
that may be, the heredity of piroplasmosis among ticks is of prime 
importance, as without it these diseases would not be contagious, 
—— 
