488 BIOLOGY OF PNEUMOCOCCUS 



cific antibodies in the serum of man following the administration 

 of pneumococcal vaccines by mouth. The preparations employed 

 comprised suspensions of pneumococci freshly killed by treatment 

 with hydrochloric acid; suspensions of the same organisms after 

 desiccation ; bile solutions, sometimes filtered, of the cocci ; and 

 dried and pulverized preparations of these solutions. In addition, 

 in some experiments, Ross fed to the human subjects living pneu- 

 mococci either dried and contained in capsules or suspended in 

 water. The results of the later experiments on human beings re- 

 ported by Ross may be epitomized thus : Vaccines administered by 

 mouth in the case of Type I materials induced antibody formation 

 in 74 per cent of fifty-three persons, seven of whom required two 

 series of feeding, while in fourteen other persons no protective an- 

 tibodies appeared after two series comprising ten feedings. Sixty 

 per cent of individuals receiving Type II antigens developed anti- 

 body, while eleven of the subjects failed to react, although five 

 were given two series by ingestion. With Type III, the results 

 were difficult to evaluate since antibody production was slight and 

 irregular. The content of antibody in the blood of men orally im- 

 munized was low and was similar in degree to that of convalescent 

 blood, while variations in the amount of antibody were observed in 

 different individuals. Ross noted heterogeneity of the antibodies 

 appearing as a result of vaccines administered orally, especially 

 with those derived from Type II organisms. The duration of the 

 immunity developed after the ingestion of the various preparations 

 was approximately seven to fourteen months, but the experimental 

 evidence bearing on this phase of the subject is not complete. Ross 

 recommended as a practical procedure the use of completely au- 

 tolyzed cultures, because he believed that autolysates contain sev- 

 eral times as much antigenic material as eighteen-hour cultures of 

 cocci in broth. From all that we know of the antigenic integrity of 

 the components of Pneumococcus, it is difficult to subscribe to this 

 recommendation. 



During the period in which Ross was prosecuting his studies, 



