viii AGGLUTINATION OF B. PESTIS 243 



used was not great, yet a comparison with normal blood 

 proved conclusively that the test with plague blood is 

 distinctly of value. 



I have recently had occasion to test the blood serum 

 of two monkeys which had been previously protected by 

 injection of my organ prophylactic (see later), and had 

 then been tested for immunity by subcutaneous injection 

 of virulent B. pestis. Fourteen days after the sub- 

 cutaneous injection of a multiple fatal dose of virulent 

 B. pestis into the previously protected monkeys, and 

 which injection caused no abnormal symptom of any 

 kind, the blood of these monkeys was tested on salt 

 emulsion of B. pestis. To three drops of the emulsion a 

 small loop of the blood serum of monkey 1 was added, 

 the proportion of serum to emulsion was about 1 : 20. 

 After twenty minutes there were distinct signs of 

 agglutination ; after thirty minutes agglutination was 

 striking and complete, all the bacilli of the emulsion 

 having become massed together into smaller and larger 

 clumps. The blood serum of monkey 2 used in the same 

 way acted also distinctly but not quite so markedly as 

 that of monkey 1, since here, even after one hour, 

 agglutination was not complete, although numerous 

 smaller and larger clumps could be met with. 



