1 Nov., 1897.] QUEENSLAND AGRICULTURAL JOURNAL. 411 
is some essential difference in their blood, and analogy suggests that this 
difference depends on the presence of some kind of anti-toxic substance. The 
long persistence of the microparasites in the blood of recovered animals—as 
witness the Washington cow—might, at first sight, seem to suggest that if any 
such substance is present it can only be of slight protective efficacy. ‘This 
does not follow from the premises, however, because it is well known that even 
so potent an ant?-toxin as that produced by the vital resistance of the horse in 
response to the irritation of the poison of the diphtheria bacillus—z.e., 
diphtheria anti-towin—has no destructive actiou on that bacillus itself, but only 
antagonises, or in some unknown way neutralises, the poisonous toxins which 
the bacillus generates. 
The question of hereditary immunity, though beyond the scope of the 
present paper, is of such great importance that a few words may perhaps be 
permitted on the subject. What grounds have we for thinking that calves born of 
immune parents will be immune? Only, in the knowledge of the writer, a single 
observation to the effect that the specific microparasites (extra-corpuscular?) 
were detected in the blood of a fatal calf from a cow that died from 
artificially induced tick fever. The authorities of the Washington Bureau of 
Animal Industry are of opinion that there is no evidence to prove that the 
progeny of cattle in the permanently infested districts are hereditarily immune, 
but consider that the calves are probably inoculated so young and so 
constantly in such localities, that they become immune. ‘The facts of the 
matter can only be ascertained by a series of careful. experiments. And 
the only information that the present writer can contribute on this subject 
is that the blood of a foetal calf, five or six months old, taken from a cow that 
was killed in an advanced stage of acute tick fever at the Hughenden experi- 
mental yards, showed no tick-fever organisms, either free or within the 
corpuscles ; and, further, that 24 c.c. of this blood, injected beneath the skin 
of a susceptible cow, caused no rise of temperature; whilst 2 ¢.c. of the 
mother’s blood, injected at the same time, for control purposes, into a second 
susceptible cow, set up a typical attack of tick fever. Very great importance 
cannot, however, be attached to any single observation of this kind, whether it 
seems to support or to refute the theory of hereditary immunity. If the cow 
which failed to react to the injection of fatal blood should, nevertheless, prove 
to have been protected by it, it might, perhaps, under the circumstances, be 
held to suggest that hereditary immunity, if it exists, may be brought about 
rather by the transmission of acquired (azti-towic) modifications in the blood of 
the mother, than by the direct transmission of the micro-organisms of the disease. 
It might also be held to warrant the hope that the milk of immune cows may 
possess protective properties, as is known to be the case in respect to the milk 
of some animals immuned to other diseases. 
Looking at the whole subject of inoculation for tick fever, it will be seen. 
that, though the prospect may fairly be called brilliant, it cannot as yet be 
accurately defined on account of the penumbra of unsolved problems by which 
itis surrounded. The observation of yesterday is often contradicted by that 
of to-day, and the inferences that to-day seem well grounded have, to-morrow, 
to be modified by the light of fresh knowledge. This sketch must, therefore, 
be regarded only as an attempt to represent the aspects of the subject as they 
appear at the present time. 
Hughenden, 
9th September, 1897. 
