348 QUEENSLAND AGRICULTURAL JOURNAL. [1 Sepr., 1901. 
Tt will be seen that there is no difference between this animal, which was 
inoculated twice in succession, and those which were only inoculated once. 
The hematozoa which were injected on August 6 evidently found the 
organism inimical to their natural development ; it was a case of true immunity, 
not one of tolerance. 
There can be no doubt that after an inoculation with malarial virus, Nicolle 
and Adil-Bey saw the hematozoa re-appear in the blood of cattle which they 
considered refractory. But this phenomenon is probably due to these learned 
experimenters operating ou animals which an insufficient or too ancient 
immunity did not protect from a mild attack. 
I have correctly shown in the course of this study, that after some months 
cattle affected with benign malaria find their sensitiveness returning by degrees 
in presence of the Piroplasma. 
I will now explain how I understand immunity in bovine malaria. 
SUMMARY OF THE MECHANISM OF IMMUNITY IN BOVINE 
MALARIA. 
LATENT PARASITISM AND CONSTANT IMMUNITY. 
Clinical and experimental science demonstrate in an irrefutable manner 
that a first attack of bovine malaria confers immunity. 
This immunity is correlative with the intensity of the infection. 
Tt will be all the more lasting the more severe has been the attack. 
So far, its duration has not been well determined. Jn order to determine 
it in as exact a manner as possible, I havemade some experiments in re-inocula- 
tion of cattle which have been cured of the virulent form for two, four, six, 
and eight months, and which had not undergone, in all that time, any fresh . 
inoculation, either natural or experimental. 
All these animals resisted the trial inoculation without experiencing the 
least discomfort. 
Although my experiments have not been carried out on animals which had 
recovered longer than eight months, it is extremely probable that immunity 
acquired by a virulent attack, either experimental or natural, lasts much longer.* 
Is it possible, with the knowledge which we possess to-day of the biology 
of the Piroplasma bigeminum, to penetrate further into the study of this refrac- 
tory condition, to understand better the mechanism of this resistance offered by 
the organism to a fresh attack? There appears to me to exist in the solution of 
this problem a question of doctrine of considerable importance. 
The discovery of the complete cycle of evolution of the Piroplasma 
bigeminum will help us to interpret the mechanism of immunity in bovine 
malaria. To thoroughly understand it, we must first study it amongst animals 
which have been diseased by experimental means. The refractory state then 
presents itself in all its purity, completely disengaged from outside influences. 
The experimental researches to which I have devoted myself, justify me 
in affirming that the Piroplasma bigeminum does not act in the organism of 
cattle by its sole presence in the blood corpuscles. It has evidently also the 
property of secreting a poison more or less analogous to the toxin of microbes 
by the help of which poison it causes, in some manner, the substance of the 
blood to ferment in order to assimilate those parts useful for its development. 
The chemical analysis of blood, without indicating to us the nature of this 
poison, has, at least, shown us some of its effects, such as a greater solubility of the 
albumen and of the hemoglobin, and destruction of a large portion of the latter. 
In diminishing the corpuscular resistance, this hwmatozoic poison fayours 
the development of the Piroplasma in the interior of the blood corpuscles. 
The infection continues its ravages so long as there are corpuscles sensitive to 
the action of the poison, and in condition, consequently, to be invaded by the 
micro-organism. 
*Ttis my intention to complete these experiments on animals which recovered a year or 
more ago, 
