8. In dealing with such obscure questions as these, three 

 methods of enquiry, should be utilised, and to fche fullest 

 extent possible, because each depends on the other two for its 

 success. These are — experiment, controversy and reconstruc- 

 tion of knowledge. The need for continued research is obvious 

 if we are to learn the true principles which determine the produc- 

 tion of a good therapeutic serum for parasitic bacteria, and how 

 its mode of action is to be explained. About these matters 

 there is much dispute, and it is the proper function of scientific 

 investigation to elucidate them. Immunity is a very young 

 science ; it has not yet acquired a solid basis of immutable 

 principles, but has to depend on current theories which are 

 really no more than working hypotheses. It often happens 

 that the immediate result of controversy about a difficult 

 question is merely to emphasise the fact that the contro- 

 versialists cannot come to an agreement because they are 

 relying on hypotheses which are different and apparently 

 irreconcilable. Thus the qualities of a good serum are explained 

 in a variety of ways, the discussion of which necessarily involves 

 the use of technical terms and leads to questions as to whether 

 the true explanation is to be found in a precipitin, a bacteriotropin, 

 a bacteriolysin, an anti-endotoxin, or an anti-aggressin, and so 

 forth. These theories cannot all be right — so what is to be done 

 with them ? If it were possible to take them seriatim and show 

 that, in relation to a concrete problem such as pneumococcal 

 immunity, each of them, except one, is wrong, the matter would 

 be simple. This, however, is not practicable, because most of 

 these theories contain some element of truch and therefore 

 simplification cannot be effected by the method of exclusion. 

 But something may be done by attempting to reconstruct some 

 of these current conceptions about the principles of immunity ; 

 and that this should be done is a matter not of choice but of 

 necessity, because these questions are of immediate practical 

 importance to the immunologist and cannot be allowed to remain 

 " held up " indefinitely on the horns of academic dilemmas. 



9. The purport of the third report in this volume is 

 accordingly to aid in the adjustment of ideas as to the signifi- 

 cance of certain serological reactions. The practical importance 

 of this question in relation to pneumococci is due to the fact that 

 special peculiarities of these organisms appear to involve great 

 difficulties in the preparation of useful therapeutic sera. These 

 difficulties are not likely to be overcome unless further light can 

 be thrown on the nature of those reactions between a micro- 

 organism and its animal host which lead to the production of 

 immunity against parasitic bacteria. 



10. Dr. Scott's report provides useful material for comparison 

 between the pneumococcus and Pfeiffer's bacillus of " influenza." 

 Both organisms are very common inhabitants of the upper 

 respiratory passages and are very frequently non-pathogenic, 



x 17680 b 



