720 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
tion through the different evolutionary stages of the ticks (egg, larva, 
nymph, and adult) the sporozoan does not itself undergo a series of 
transformations more or less comparable to those undergone by the 
paludic plasmodium in the body of the mosquito. Probably, then, 
this evolution can only reach the final stage (which is the formation 
of spores that are still hypothetical because they have not been seen) 
in the organism of the adult ticks. It could thus be explained 
why the larvee and nymphs are incapable of inoculating the disease. 
They contain only the piroplasms at an intermediate stage, in which 
their inoculation into vertebrates would be insufficient to reproduce 
the affection. 
Here, again, the hypothesis of a development is rendered more 
probable by comparison with the facts regarding the hemogregarines 
of the tortoise shown by Siegel. As we have already said, the 
sporozoans perform a true evolution in the leeches with the forma- 
tion of eggs and spores, and this scarcely leaves any further doubt 
regarding the reality of a similar evolution of the piroplasms in the 
-body of the acarian,. 
To summarize, we ought, indeed, to recognize that it is stijl un- 
known how the young female ticks of infected mothers propagate the 
disease. It is probable that the spores exist in the salivary glands, 
but it has not been possible to establish this so far. As we said at the 
beginning of this chapter, the intimate mechanism of the ixodian 
transmission still remains mysterious in many respects. Nevertheless, 
there is not a single reason to deny this transmission itself, which is 
demonstrated by so many facts, as some still do. 
Such is the real relation of the arthropods to pathology. Without 
doubt, unfortunately, the list of dangerous species is far from being 
complete, and the redoubtable faculty of propagating diseases does 
not belong exclusively to those animals in’ which it has been recog- 
nized thus far. | 
In closing, I would inquire whether the discoveries which I have 
recalled, and which have so great an interest from the point of view 
of pure se ience, have not already had some practic: al effect on prophy- 
laxis. Fortunately, one is able to say that it is due to them that 
protection against diseases can be turned entirely in another direc- 
tion than has been done. Owing to them, one can understand that, 
in order to be established on a rational basis, the combat againgt 
these affections should take note of two thingss first, the destruction 
of biting arthropods wherever it is possible, and to as great an extent 
as possible; second, the protection of man and the domestic animals 
against the attacks of those which escape this extermination. 
To give an idea of the results which can be obtained by the system- 
atic practice of these two principles we will recall in a few words 
