Acquired immunity against micro-organisms 269 



immunity. Both resist about the same temperatures; both are 

 found in the blood plasma and pass into the fluids of exudations 

 and tran sudations. But it may be affirmed with certainty, as already 

 stated, that the two properties are quite distinct. Pfeiffer has laid 

 great stress on the fact that highly protective serums often exhibit 

 only a feeble agglutinative power and vice versa. During an in- 

 vestigation 1 into an epidemic of typhoid fever, he had occasion to 

 study the serum of patients convalescent from this disease. The 

 exact dosage of the two properties demonstrated that a slightly 

 marked agglutinative property might be associated with a very 

 powerful protective property. Gheorghiewsky 2 made similar obser- 

 vations on animals vaccinated against the Bacillus pyocyaneus. 

 The serum of a goat, although more agglutinative, invariably proved 

 to be less protective than that of a rabbit. A similar result 

 was obtained with the serum of immunised guinea-pigs. "This [283] 

 shows distinctly " concludes Gheorghiewsky " that the property 

 possessed by serums of agglutinating the Bacillus pyocyaneus does 

 not march parallel with the protective property " (p. 304). Analogous 

 examples are sufficiently numerous to justify us in accepting the 

 distinctiveness of the two properties of specific serums. 



The protective or anti-infective substance is, therefore, not the 

 same as the agglutinin. But are we justified in regarding it as 

 identical with the fixative substance, or fixative (sensibilising sub- 

 stance, immunising or intermediary substance, or amboceptor) ? From 

 the fact that the fixative was at first rightly designated by Bordet 

 as protective substance we should conclude in the affirmative. The 

 question is an important one and merits close examination. The 

 discovery of an exact method of determining the presence of 

 fixatives has rendered it possible to ascertain whether these sub- 

 stances are always found in the protective fluids and also whether 

 the presence of fixatives necessarily implies the protective power 

 of the serums. 



The first of these questions has been answered in the affirmative. 

 All the protective serums studied from this point of view, by Bordet 

 and Gengou> were found to be endowed with very distinct fixative 

 properties. They also found the specific fixative in the serum of 

 guinea-pigs immunised with the attenuated bacilli of the first vaccine 

 of Pasteur. Now this serum is powerless to prevent the production 



1 " Typhusepidemien und Trinkwasser," Jena, 1898, S. 26. 



2 Ann. de I'Inst. Pasteur, Paris, 1899, t. xin, p. 298. 



