PNEUMOCOCCAL VACCINES 481 



properties as may have occurred in the process of preparation. In some 

 preparations the organisms are sensitized by appropriate treatment 

 with homologous immune serum. 



2. Extracts of pneumococci made in water, saline solutions, bile or 

 bile salts, and other solvents, freed from cellular elements and contain- 

 ing the substances of the bacterial cell soluble in these solutions. In the 

 preparation of extracts, autolysis of the cocci may or may not have 

 occurred. 



3. Autolysates of pneumococci taken at different stages of self-diges- 

 tion of the coccal bodies and usually cleared of formed cellular material 

 by Berkefeld filtration or some other method for removing particulate 

 matter. 



4. Solutions of the various chemical components of the pneumococ- 

 cal cell isolated from supposedly non-antigenic substances. The solu- 

 tions may be composed of only one constituent or of two or more sub- 

 stances derived from the cell. In the case of these solutions the question 

 should be borne in mind how closely the ingredients approach the anti- 

 gens as they exist preformed in the living and fully functioning viru- 

 lent bacterial body or, conversely, to what extent their molecular struc- 

 ture has been changed by the manipulations required in manufacture. 



In the present chapter attention will be directed chiefly to the 

 preparation and the immunizing effect of those vaccines that have 

 been employed for prophylaxis or therapy in man. The rationale 

 of the use of pneumococcal vaccines is based on two kinds of evi- 

 dence: the result of prophylactic injection in experimental ani- 

 mals, and the effect of vaccines in the prevention and cure of spe- 

 cific infection in human beings. 



EXPERIMENTS ON MONKEYS 



The previous chapters of this volume are replete with references 

 to the capacity of Pneumococcus or its derivatives to induce in 

 mice, rabbits, and other domestic animals the formation of specific 

 antibodies contributing to the immune state. The earlier experi- 

 ences in which the monkey was the test animal, because of the 

 closer zoological relationship of that species to man, are perhaps 

 the most significant in estimating the probable effect of the appli- 



