CHAPTER XVII 

 UNSOLVED PROBLEMS 



Impressive as is the progress that has been made in Pneumococ- 

 cus research, the subject holds almost endless possibilities for 

 further investigation. Some of the metabolic activities of Pneumo- 

 coccus, the processes operating in dissociation and type transfor- 

 mation, the exact chemical composition and precise antigenic 

 properties of the pneumococcal cell, these are subjects, among 

 many others, calling for continued study. 



It is probable that the heights which may be achieved in the pro- 

 duction of artificial immunity to Pneumococcus in man and in 

 serum-producing animals have not been reached. Antipneumococ- 

 cic serum, at best, leaves much to be desired in the way of purity 

 and potency. There are many inviting leads and, with the applica- 

 tion of rapidly developing chemical and serological methods, the 

 years to come should be even more fruitful than those of the past. 



TOXINS 



The idea persists, in spite of many disappointing failures, that 

 some of the symptoms incident to pneumococcal infection, espe- 

 cially those of lobar pneumonia, are caused by a soluble toxin. 

 The idea is a reasonable one but convincing evidence to support it 

 has never been presented. Among the varied activities of the pneu- 

 mococcal cell a substance of this nature may be produced. It may 

 exist in nascent or evanescent form or be present in such minute 

 quantities as to escape detection. Conditions that exist in the 

 animal body cannot be reproduced in full in lifeless media and 

 therefore the environment supplied by artificial culture is quite 

 different from that encountered by microorganisms in living tis- 

 sues. There is the well-known influence of specific substrates on the 

 biochemical activities and physiological processes of bacteria in 



