1 Maz., 1899.] QUEENSLAND AGRICULTURAL JOURNAL. 219 
animal. In other words, a toxin is the poisonous product of a micro-organism ; 
an anti-toxin is the protective product of a living animal to counteract it. The 
more toxin is introduced into an animal the more anti-toxin is produced to 
counteract it. So that the blood of an animal into which large doses of toxin 
have been introduced becomes very rich in anti-toxin—so rich that when injected 
into a susceptible animal it protects it, too, in a passive way from any toxin 
which may be injected into, or generated in, its blood. This is the ratzonale of 
the diphtheria anti-toxin treatment. An injection of this serum serves not, 
only to protect for the time being a person exposed to the contagion of 
diphtheria, but, by counteracting the toxins produced by the diphtheria bacillus 
in a person actually infected with diphtheria, acts essentially as a curative 
agent. - 
r The animal in which the anti-toxin is generated is said to be actively 
immune; the animal into which the serum of such an animal is injected is said 
to be passively immune. That is to say, he is immune only as long as the anti- 
toxin (which was manufactured in the body of thé actively immune animal) 
remains in his system. When it is eliminated, he loses his immunity ; passive 
immunity is, therefore, only a temporary affair, but, for practical purposes, one 
of the very greatest importance. 
In some cases the serum of an immune animal is, as above described, 
anti-toxic only—that is to say, it only antagonises the toxins produced by 
micro-organisms. In other cases it is also “ anti-microbic”—that is to say, 
it destroys the micro-organisms themselves. In the case of ‘Texas fever, the 
serum of recovered animals can be only anti-toxic, because, as we know, it does 
not destroy the micro-organisms in the blood of such animals. 
All this is, I am sure, quite familiar to you, but I have gone over it again, 
as it is essential to the plan I am trying to work out. If I am correct in 
assuming that the cause of immunity to Texas fever is the presence of an anti- 
toxin in the blood of recovered animals, then the Jarger the dose of “‘ recovered ” 
blood injected, the Jess should be the reaction produced; because the quantity 
of anti-toxin contained in a large dose of such blood would have some effect 
in counteracting the toxins produced by the microparasites introduced at the 
same time. The number of microparasites introduced at the time of the 
injection probably makes little difference, because, be they few or many, they 
will, from their power of multiplication, in a short time reach the possible 
maximum, which is determined by quite other factors than the number 
originally introduced. Hence a dose of 500 c.c. of ordinary recovered blood 
should produce less reaction than 5 c.c. of the same blood. JI think, probably, 
it would produce no reaction at all, but would probably afford a passive 
immunity of short duration. J have never yet gone so high as 500 c.c., however, 
but intend shortly to do so. But for general use such large injections would 
be obviously impracticable. Moreover, they would be undesirable (if they were 
found to have the action indicated), because we desire to set up a certain degree 
of reaction which shall be followed by active and therefore lasting immunity. — 
Tf, however, we could find a means of very greatly enhancing the anti- 
toxic power of the blood of a recovered animal, so that a comparatively small 
quantity of it would have the same counteracting or protective effect, as I have 
suggested, of 500 c.c. of ordinary recovered blood, we should be able to use it. 
as a means of regulating the reaction caused by inoculation with virulent blood 
—and perhaps also as a curative agent in the early stages of the natural disease, 
The means by which I am hoping to obtain this more potent anti-toxic 
blood (we should be able to separate the serum and bottle it off for use 
as required, as is done with the anti-diphtheritic serum from the horse) is by 
repeatedly injecting into the jugular vein of a recovered animal very large doses 
of the most virulent Texas fever blood I can get. Beginning by injecting 
100 ¢.c. of virulent blood into an animal that had completely recovered from the 
inoculation fever, I intend to repeat the injections at intervals up to 500 c.c. 
of virulent blood. And by this means I hope to enhance or enforce the anti- 
toxic value of its blood toa very great extent. . 
) 
