SERUM TREATMENT OF LOBAR PNEUMONIA 599 



der them susceptible to the attack of the natural protective forces 

 of the body. The chapters on antigenicity (X), antibody forma- 

 tion (XI), and host response (XII) enumerate the several anti- 

 genic elements of the pneumococcal cell with their common or indi- 

 vidual characters, trace the activity of these constituents in the 

 animal economy, and describe the nature of the antagonistic sub- 

 stances thus created. 



Problems and Limitations of Serum Therapy 



The immunologist has succeeded in raising the antibody content 

 of the serum of experimental animals to a level high above that en- 

 gendered by spontaneous pneumococcal disease in man, but specific 

 immune serum, even though it be rich in these protective principles, 

 cannot convey to the recipient those less tangible properties ac- 

 quired by the tissues as a result of antigenic stimulation. This 

 failure constitutes one limitation of serum treatment. 



The variety of serological types of Pneumococcus presents an- 

 other complication, since the serum to be effective must correspond 

 in type to the organism causing the infection to be treated. Anti- 

 pneumococcic serum, therefore, does not have the broad immuno- 

 logical species-specificity of diphtheria or tetanus antitoxin ; its 

 affinities are strictly specific for type. Moreover, no matter how 

 rich in type-specific antibodies a serum may be, when the mass of 

 infecting pneumococci exceeds a given amount — all other condi- 

 tions being equal — the serum is powerless to stop the multiplica- 

 tion, invasion, and subsequent malignant activities of the organ- 

 isms within the infected host. The interaction of antibodies and 

 pneumococci does not operate strictly according to the law of mul- 

 tiple proportions, and this relation between concentration of 'spe- 

 cific antibody and living pneumococcal cells may determine the 

 outcome of the infection. There are variations in this relation 

 which are not yet understood. The ratio of amount of antibody to 

 number of cocci is lower for Type I than for Type II. The utter 



