75 



that this is the case. On the other hand, the persistence of type 

 in prolonged subculture does not show that mutation cannot 

 occur in the living body. 



The " mosaic " theory is of special interest because a highly 

 elaborate explanation of pneumococcal antigens and antibodies 

 has been based upon it. But there are many investigators 

 who do not support this explanation, and it appears to me that 

 the conception of a large and intricate mosaic pattern is not 

 applicable to pneumococci and their antibodies. In fact, 

 pneumococci seem less amenable to the " mosaic " idea than 

 certain other bacterial species amongst which different strains 

 or races show serological interrelationship. 



Coming now to physical conditions in relation to immunity, 

 these, no doubt, play an important part in the reactions between 

 pneumococci and the living body; but they are involved in so 

 much obscurity that it may appear questionable whether any 

 profit can arise from discussing them. If satisfactory therapeutic 

 sera for pneumococcal infections were available, and if their 

 action could be shown to be due to demonstrable antibodies, 

 discussion of these physical factors might be relegated to the 

 more or less negligible class of " merely speculative " ideas. But 

 these desirable results have not yet been attained, though further 

 progress is to be hoped for. It may be possible, for example, to 

 discover an antitoxic serum which will neutralise the toxic effects 

 of pneumococcal invasion. 



Meanwhile, in answer to the question which forms the subject 

 of this report, I think the study of serological differences amongst 

 pneumococci has not led to any final conclusions such as would 

 justify the opinion that no serum wiN be therapeutically 

 efficacious unless it contains an antibody corresponding to the 

 antigen which is peculiar to the infecting strain. 



Other sides of the question need consideration, into which 

 factors of a physical as distinct from a purely chemical nature 

 appear to enter. What is the significance of the bacterial capsule 

 and of the mucinous material derived from disintegration of the 

 capsules ? A great deal has been written about " aggressins," 

 " anti-aggressins," and " antiblastic immunity " ; though these 

 particular terms have dropped out of favour, the problems which 

 they raise are of importance and are still unsettled. Then there 

 are questions of cell permeability, as affecting capacities for 

 bacterial invasion and as determining, on the part of the host, 

 conditions which permit of the escape of antibacterial substances 

 from leucocytes or other cells. Questions such as these, into 

 which I have not entered in this report, cannot be settled by 

 limiting the enquiry to a search for chemical affinities between 

 antigens and antibodies. 



My general conclusion, therefore, is that Neufeld's views 

 about the significance of serological differences amongst pneumo- 

 cocci ought not to be accepted as final, though it must be admitted 

 that the difficulties which these serological differences involve 

 have not yet been overcome. 



