71 



these bacteria. This view is still popular, though there has 

 been a good deal of dispute as to whether the phagocytes kill 

 the pneumococci or devour them after they have been killed 

 by some other means. Into this subject I have not attempted 

 to enter in this report. As it will probably be a long time before 

 any general agreement is reached on the importance of bacterio- 

 tropins and leucocytes in pneumococcal immunity, it would be 

 unwise to await a decision on this point before considering other 

 aspects of the question. Help might be derived from any 

 differences or resemblances which can be demonstrated between 

 acquired and natural immunity towards pneumococci. 



Another question may be worth raising. If the more orthodox 

 views about the significance of antibodies have to be modified, 

 will any modification be needed in the current distinction between 

 a vaccine, which is assumed to act as an antigen, and an immune 

 serum, which is supposed to confer passive immunity by virtue 

 of its antibodies ? With certain bacterial parasites it has been 

 found that, in order to produce a therapeutic serum, the animal 

 must be drenched with bacterial " antigen " long after the stage 

 of active immunity has been reached. May not this treatment 

 lead to the presence in the serum of some substance, perhaps a 

 modified bacterial colloid, possessing the therapeutic property 

 of a vaccine specially prepared so as to stimulate resistance 

 promptly ? This may possibly be the case with the serum 

 prepared by Preston Kyes (see pp. 14-16 of my preceding report). 



Summary and Conclusions. 

 Method. 



In reading literature on immunity it is found that most 

 questions bristle with a perplexing variety of hypotheses, which 

 cannot all be right. What is the best way of trying to get at the 

 truth with the least possible delay? There are at least four 

 methods of recording scientific progress ; these are all useful and 

 necessary, and they supplement each other. For convenience, I 

 take them separately, though it is obvious that a writer may 

 employ more than one. 



(1) The investigator sets out his evidence in support of the 

 hypothesis which he favours and then leaves his work to speak 

 for itself, on the assumption that, in course of time, the weaker 

 hypotheses will be neglected and the strongest will survive. 

 In the case of a very brilliant piece of research, this method is 

 successful. But, in the more common event of many rival 

 contributions, no one of which is obviously pre-eminent, it takes 

 too long to wait for the truth to speak for itself, on the principle 

 of the survival of the fittest. 



(2) The investigator not only pleads his own case, but 

 endeavours to refute the arguments of his opponents. 

 Scientific controversy, of course, is the most valuable way of 

 clearing up the truth. The only trouble is that, as controver- 



