76 INFECTION AND RESISTANCE 



specific treatment with bacteria or their products. The moderately 

 beneficial effects of the various antiplague sera and the limited suc- 

 cess attending the use of antistaphylococcus, antistreptococcus, and 

 antipneumococcus sera probably depend, as recent work tends to 

 show, not upon the direct action of antitoxic bodies, but rather upon 

 the indirect opsonic action 62 1(i3 64 65 which renders the bacteria 

 more easily amenable to phagocytic action. These points we shall 

 discuss at greater length in a succeeding chapter. 



SPECIFICITY 



In speaking of methods of immunization in the preceding sec- 

 tions we have frequently employed the terms ''specific" and ''spe- 

 cificity," without sufficiently defining them. It will be necessary to 

 explain them since the principle of specificity is at the same time one 

 of the most important and one of the most mysterious of the phe- 

 nomena of immunity. When an individual has recovered from an 

 attack of typhoid he is thereafter immune to typhoid but to no 

 other disease similarly with plague, cholera, small-pox, etc. The 

 same principle governs artificial immunization. Vaccination against 

 anthrax protects against anthrax only and active or passive im- 

 munization in any of the infectious diseases produces a resistance 

 which is "specifically" aimed only at the particular infectious agent 

 w r ith which the original active immunity was produced. The prin- 

 ciple points to an exquisite chemical difference between the protein 

 substances which constitute the bacterial cell bodies or their meta- 

 bolic products. For although by chemical methods we can detect no 

 differences between them yet the reactions of immunity are sharply 

 differentiating. When we come to consider the antibodies which 

 specifically precipitate the substances by which they are incited we 

 shall see that the delicacy and consequent differential value of these 

 reactions far outstrip any known chemical methods, and it is upon 

 this principle indeed inexplicable as it is that the great diagnostic 

 value which these reactions have attained depends. The conception 

 of the specificity of the causes of infectious disease, as well as that 

 of the specificity of toxins, has become so common and self-evident 

 to us that we are too apt to forget how fundamental to progress the 

 establishment of this fact was in the early days of bacteriological 

 research. When, in 1878, Koch published his treatise on the "Eti- 

 ology of Wound Infections" specificity was not generally accepted, 

 and the supposed metamorphosis of bacterial species, as asserted by 



62 Neufeld. Deutsche med. Woch., No. 11, 1897. 



63 Neufeld and Rimpau. Deutsche med. Woch., No. 40, 1904. 



64 Bail and Kleinhans. Zeitschr. f. Imm., Vol. 12, 1912. 



65 Weil. Zeitschr. f. Hyg., 75, 1913. 



