454. QUEENSLAND AGRICULTURAL JOURNAL. [1 Dzc., 1898. 
The principle of protective inoculation in general need not detain us. 
Broadly stated, and omitting all exceptions and reservations, it rests upon the 
facts: (1) That one attack of an acute infective disease confers protection 
against subsequent attacks; (2) that such disease can be communicated 
artificially by inoculation from one animal to another; (8) that the attack 
produced by this means is less severe and dangerous than when the disease is 
contracted in the ordinary way; and (4). that, like an attack of the naturally 
acquired disease, it confers protection against subsequent attacks. The process 
is subject to many modifications, but its efficacy in regard to many ills of man 
and beast is thoroughly established, and the success of its application in the 
case of Texas fever has now been very amply proven. 
I would not be misunderstood, however. When I say that inoculation 
has been proved a satisfactory protective against any given disease, I do not 
mean to imply, either that it necessarily confers as complete protection as an 
attack of the natural disease, or that it is absolutely effective in every case 
operated on. That would be too much to expect, or is, at anyrate, more than 
the facts warrant. The degree of protection afforded by inoculation against any 
given disease is, probably in most cases, directly proportionate to the severity 
of the reaction produced, ‘Take the well-known case of smallpox. A person 
who has passed through a severe attack of the disease, contracted in the ordi- 
nary way, is rendered immune for the rest of his life. One who has been 
inoculated after the old-fashioned method, directly from a smallpox pustule, is 
also rendered very highly immune, but probably somewhat less so than in the 
previous case ; and one that has been vaccinated by the mild modern method 
with smallpox virus that has become attenuated by passing through a series of 
bovine animals, still less—so that the process in this case may have to be repeated 
at intervals; and even some few vaccinated persons may contract smallpox. 
In this case it is evident that the milder the inoculation disease the less is the 
subsequent protection. And I thinkit is probable that the same thing applies 
in other diseases. We do not, however, because of occasional failures, say that 
vaccination generally is a failure ; on the contrary, in spite of these things, we 
regard it as an eminent success, inasmuch as it has practically stamped out one 
of our most dreadful diseases. And it is the same kind of relative—not abso- 
lute—success that I claim for indculation as a protection against Texas fever. 
Texas fever, however, differs (2?) from the ordinary infective diseases in 
this—that the microparasite, like the corresponding organism of malarial fever, 
remains in the blood long after the acute disease has passed away, a circum- 
stance which explains the effectiveness of the blood of recovered animals for 
inoculating purposes. Sometimes its persistence causes a chronic wasting form 
of disease, as does also the malarial parasite in man. More generally, however, 
it causes no symptoms whatever, and “recovered” cattle return, more or 
less quickly, to perfect health and condition. And though the survival of the 
microparasite in the blood is unquestionably of very conimon ovccurrence— 
whether if has been originally introduced by the tick or the syringe—I am not 
certain that this invariably happens. The most searching test—and by far the 
most reliable one—as to whether the blood of any particular recovered animal 
contains the Texas fever parasite or not, is to inject some of it into a 
susceptible animal, or into a number of susceptible animals, and observe if any 
fever is produced. Certain it is that the blood of different recovered animals 
varies very greatly in its fever-producing power. ‘The blood of some such 
animals has been found not to have this power ; from which it is reasonable to 
infer that it contained no microparasites. For this reason 1 should, be inclined 
to recommend that only recovered animals whose blood has been actually 
proved by the injection test to have the requisite power of setting up fever 
should be used for inoculating purposes—at any rate, when the inoculations are 
to be done on a large scale, and cannot be easily repeated in case of failure to 
produce reaction. It is a very simple thing to inject a few susceptible cattle 
with the blood proposed to be used, and thus obtain definite information as to 
its suitability, or otherwise, for further inoculations, 
