PRODUCTION OF ANTIPNEUMOCOCCIC SERUM 537 



Whichever schedule of injections is chosen, it has been generally 

 customary to allow a rest period of about a week between series. It 

 is possible that a longer interval might be used to advantage, but it 

 seems doubtful if shorter periods would be advisable. Barnes and 

 White 86 observed that in rabbits in which a primary immunity had 

 been established, rest periods of three weeks instead of the usual 

 one week between courses of injections did not lessen antibody re- 

 sponse to subsequent injections of antigen. 



The experiments of Cole (1904), 248 of Hachtel and Stoner 

 (1916), 583 and of Feemster (1932) 392 have suggested that anti- 

 body response of animals and man to typhoid vaccine is more 

 rapid and vigorous in both animals and man who have either had 

 the disease or been inoculated than in those who have never been in 

 contact with the organism. The observations of Barnes and White 86 

 on rabbits under immunization against Pneumococcus bear on the 

 question. The principle involved has been applied in the immuniza- 

 tion of horses for the production of antipneumococcic serum. Un- 

 published experiments at the Massachusetts laboratory serve to il- 

 lustrate the results that may be expected in immune horses when 

 subjected to delayed secondary stimulation. A group of horses un- 

 der immunization for periods sufficiently long to establish primary 

 immunity were rested for approximately three months without re- 

 ceiving injections of any sort. Test bleedings on this group of 

 horses, taken prior to the resumption of immunization, showed an 

 average decrease of 75 per cent in antibody content during the 

 three-month rest period. After the first course of six injections 

 following the rest period, in which the total dosage of vaccine aver- 

 aged about one-fifth that of the last course, there was found to 

 have developed in the serum of the animals so treated an average 

 increase in antibody content (as compared with titers prior to the 

 rest period) of approximately 25 per cent for both Types I and 

 II. The same principle seems likely to hold true if, instead of omit- 

 ting all injections during the rest period, the horses are subjected 

 to some other form of immunization. It is open to question, how- 

 ever, whether the increased potency of serum from horses after 



