RESEARCHES ON CERTAIN PROBLEMS OF PLAGUE IMMUNITY 21 



The second animal, after a course of injection of heated filtrates, was 

 further treated with injections of filtrates of unheated cultures. In the 

 three months preceding the bleeding from which the serum tested was 

 obtained, nearly two litres of unheated toxin were injected in doses of 

 from 60 to 300 c.c. Among other toxins, nearly a litre of Toxin No. 10, 

 the tests of which have been recorded, was employed in the immunisation. 

 As already mentioned, the other horses whose sera were tested were 

 immunised by the ordinary methods. The case of the horse " Pr." 

 requires some comment. This animal had been immunised by the Berne 

 method, and had received large injections up to 300 c.c. at one dose of 

 concentrated Haffkine's Prophylactic Fluid. This was followed, as is 

 usual, by a number of intravenous injections of living broth culture. On 

 reviewing the treatment which this animal had received before the 

 removal of the sample of serum tested, it was noted that within the six 

 weeks of treatment preceding the interval which always intervenes 

 between the last injection and the venesection, the animal received the 

 following injections : — One of 40 c.c. and another of 90 c.c. of broth 

 cultures four days old, one of 100 c.c. two days old, and one of 40 c.c. 

 six days old. In regard to this, it is to be noted that these injections 

 were given rather more frequently than usual, and that 180 c.c. of the 

 material was 4 to 6 days old when at least traces of toxin might be 

 expected to be present. 



It is well known that out of a number of horses immunised against 

 diphtheria and tetanus toxins, only a certain number of these respond 

 freely and quickly to the stimulus of toxin injections, and are capable 

 of producing antitoxins of the highest potency. It is probable that this 

 variability among the individuals of the same species, in the response to 

 stimulation by toxin, may extend to other forms of immunisation. It is 

 quite conceivable that the dosage mentioned may have in this case been 

 a sufficient stimulus to excite the mechanism necessary for antitoxin 

 production in a highly responsive organism. 



To ascertain whether the injection of heated filtrates had given rise 

 to antitoxin production, the following preliminary test was carried out 

 with the serum of horse " R," and controlled with the serum of normal 

 horse "Z," the test toxin employed being Toxin No. 10. The toxin 

 and serum were mixed and kept one hour at 35° C. It will be seen in 

 Table XII. that the evidence is in favour of antitoxin production. 



(131) K I 



