1 Dec., 1898.] QUEENSLAND AGRICULTURAL JOURNAL. 451 
overcome in the vicissitudes of its subsequent pilgrimage: the sun may have 
been too hot, the shade too scanty, the weather too cold or too dry, the soil or 
pasture in some way unfavourable, or the young tick too long in finding a 
bovine host. Under any of these circumstances it seems conceivable enough 
that the microparasite, which we know to be a very sensitive organism, might 
pine and die before reaching its natural destination in the blood of some other 
bullock. Again, the young tick might convey its charge to some unsuitable 
host, in which it could not develop—such as horse or sheep—and, in that way, 
rid itself of its burden, or, as we generally call it, its contamination; and thus 
a race of non-fever producing ticks be established. For it is difficult to 
believe—and has, at any rate, not so far been satisfactorily proved—that ticks, 
which have matured upon naturally insusceptible animals (¢.¢., non-bovines), 
can acquire from them and transmit to their progeny the germs of the disease. 
Though I am aware that it might be suggested that a germ-bearing tick, 
maturing on such a host, might still be able to retain and transmit to its 
progeny the germs of the disease which itself received from its parents, by a 
kind of hereditary transmission of virulence akin to the reproduction process 
called parthenogenesis, where the impregnation of a single female sutlices for 
the fertilisation of many successive generations. 
But I do not think that we have any evidence to warrant the supposition 
that there is any such intimate bond of union between the microparasite and 
the tick. On the contrary, I should say there are good grounds for thinking 
that the bond is a comparatively loose one, and that ticks lose the contamination 
with considerable facility. For it is difficult otherwise to account for the fact that 
ticks that were certainly, directly or remotely, derived from contaminated 
cattle, have altogether failed to produce any Texas fever in certain localities 
into which they’ have been carried, even though they have increased and 
multiplied for many generations, and have become enormously abundant upon 
the cattle in their new location. It would seem also that ticks, in their onward 
march through clean herds, tend, in some way, to become dissociated from the 
fever parasite. For the ticks spread faster than the fever, and the advance 
guard has been. very frequently found not to produce the disease. Moreover 
Doctor Shroeder, of the Washington Experiment Station, succeeded in depriving 
ticks of their fever-producing power by causing each successive generation to 
mature ona fresh clean animal. ‘The microparasitic contamination appears in 
this way tu have been, so to speak, bred out of them. : 
Jt is perhaps necessary, however, that I should remind you that the views 
which Ihave just suggested, as to the part played by the tick as the transmitting 
agent of the microparasite, have not been definitely proved by exact experiment. 
They are put forward merely as hypotheses, and must in no way be regarded as 
ex cathedra opinions. I will ask you therefore to accept them only in a 
provisional way for what they may be worth, and in so far as they may commend 
themselves to your judgment. What we know for a certainty is, that the 
young tick is the agent by which the microparasite finds its way into the 
bullock ; what we conjecture is, that the adult tick is the agent by which it finds 
its way out again. But if may be said that this supposition appears to be 
supported by the illustrious Dr. Koch, who, is reported, in reference to his 
South African experiments, to have expressed the opinion that young ticks, 
to produce Texas fever, must be the progeny of ticks that have matured upon 
sick animals, ‘ 
It is conceivable, however, that the microparasite may exist in some 
unknown state or form in external Nature—in the grass, the soil, the water, or 
the air of certain localities, quite independently both of the bullock and the 
tick ; and, if this were so, it is evident that ticks might acquire the contamina- 
tion from other sources than the blood of an antecedent case of bovine infection. 
But if ticks do thus pick up the microparasite from external Nature, the 
microparasite must exist in places that are neither low-lying, coastal, nor 
swampy, for young ticks which have been hatched on high, dry, tableland country 
have very frequently communicated the disease. If they did not inherit the 
