324 BIOLOGY OF PNEUMOCOCCUS 



tations of somatic reactivity as systemic or local allergy. All the 

 phenomena depend in turn on the inherent special or racial pe- 

 culiarities of the animal subject. 



The resolution of the antigenic spectrum involves the study of 

 the effects of Pneumococcus itself, of its separate constituents with 

 their individual, chemical identification, in their relation to the 

 parent material; the diverse serological reactions in which the 

 whole cell or its parts participate ; and the nature of the mechan- 

 ism of the particular physiological response each wakens. 



These ways bristle with obstacles of one kind or another. There 

 is the tendency of Pneumococcus to digest itself or to lose its 

 vigor; there is the danger of fracturing the molecular mosaic of 

 the cellular substances by chemical treatment; there are all the 

 subtle factors which influence the interaction of antigen and anti- 

 body in the test tube ; and then there is the constitutional capacity 

 or incapacity of animal tissues to function in response to the intro- 

 duction of alien substances into the body. An antigen by one test 

 may display full power ; by another test it may seem to be incom- 

 plete or inert. Introduced in inappropriate quantity, an antigen 

 may defeat its effect ; administered by one route we see one set of 

 immune bodies, by a different route some of the antibodies may ap- 

 pear wanting type-specificity or else be entirely absent; injected 

 into animals of one species an antigen provides the animal with a 

 full complement of antagonistic substances and protects it against 

 fatal infection, while in other animals the administration of the 

 same antigenic substance may be followed by no appreciable im- 

 mune effect. Here, not only the race but the lineage, the age, and 

 the immediate physical state of the animal all have their part in 

 deciding the issue. Antigens and antigenicity, like virulence, there- 

 fore, are purely relative terms. 



First Observations of Immunity 



For a complete and orderly presentation of the manifestations 

 of the immunological behavior of Pneumococcus it seems best to 



