viii AGGLUTINATION OF B. PESTIS 203 



to which the agglutinating power of the blood can be 

 raised differs, cceteris paribus, in the different animals for 

 the different microbes ; that it differs also in regard to 

 diverse methods of administration, and again as to the 

 time at which the agglutinating power makes its appear- 

 ance. A few instances may be mentioned in illustration. 

 After intraperitoneal injection into guinea-pigs of sub-fatal 

 doses of living culture of cholera vibrio, the blood serum 

 of the animal shows some weeks later (two to three) 

 distinct agglutinating power with an emulsion of cholera 

 vibrios in the proportion of 1 : 20 or even 1 : 40. By 

 repeated (three) intraperitoneal injection of culture of 

 living cholera vibrios this agglutinating power of the blood 

 serum may be raised to 1 : 100 or even 200. I have, like 

 other persons, obtained a high degree of agglutinating 

 action by injecting subcutaneously first a large dose of 

 sterilised and then, from week to week, gradually increas- 

 ing doses of living cholera culture. A fortnight after the 

 last (fifth) injection the blood serum of the guinea-pig 

 possessed so strong an agglutinating power that one 

 part of the serum agglutinated completely, and within 

 a few minutes 200 parts of bouillon emulsion of living 

 (recent) agar culture, or, better still, a twenty-four hours 

 old peptone salt solution culture of the vibrio. 



As regards the typhoid bacillus, a high agglutinating 

 action of the blood serum of guinea-pigs can be produced 

 in just the same way. After a fifth injection the blood 

 serum agglutinates completely in the proportion of 1 in 

 400, within a few minutes, the bouillon emulsion of the 

 typhoid bacillus being made from a forty-eight to seventy- 

 two hours old gelatine culture. 



There is, however, a difference between the two 



