81 . 



pneumococci were present, influenza bacilli were often absent ; 

 but more recently this has not been so, as lobar pneumonias 

 yielding " type " pneumococci have quite frequently yielded also 

 abundant influenza bacilli. Nevertheless, of the 84 cases in 

 which both bacteria were found, 32 gave " atypical " pneumococci, 

 while of the 64 yielding pneumococci alone 12 only were 

 " atypical " : the percentages are 38 per cent, as against 19 per 

 cent. ; i.e., where the " atypical " pneumococcus was presumably 

 the exciting cause, influenza bacilli were much more likely to 

 be found than when the " type " pneumococci were concerned. 

 The suggestion is that in some cases at least the association with 

 influenza bacilli is necessary for the less virulent " atypical " 

 pneumococci to produce lobar pneumonia. Pointing in the 

 same direction is the fact that in broncho-pneumonia, which may 

 be regarded as being in many cases a pneumococcal lesion of 

 lower grade than lobar pneumonia, the pneumococcus found is 

 almost (but not quite) invariably of the " atypical " group and 

 is almost (but not quite) invariably associated with enormous 

 numbers of influenza bacilli. Experimental difficulties have so 

 far prevented me from attempting to demonstrate an enhance- 

 ment of the virulence of " atypical " pneumococci for animals 

 by association with influenza bacilli. I must therefore leave 

 the question as still sub judice. 



Serological Reactions. 

 Agglutination. 



In Table 4 cross-agglutination reactions are exhibited between 

 twelve strains of influenza bacilli and their respective sera. The 

 figures represent in each case the dilution of serum producing 

 complete deposit of the bacterial suspension, with the formation 

 of clumps which remain visible to the naked eye on shaking up 

 the deposit. In the instances where a ? is attached, the clumps 

 were of a finer kind, barely perceptible to the naked eye on 

 shaking. The titre for the homologous strain is in each case 

 printed in heavy type (see page 82). 



These cross-agglutination tests reveal certain relationships 

 and also well-marked differences between the twelve strains. 

 For example, serum Lister 3 agglutinates Fechger, L 45, S 1, 

 Rosenhain and L 1a, though in no case at dilutions higher than 

 1 in 400. With the other strains this serum produces either 

 no agglutination or fine agglutination disappearing on shaking. 



The sera Self 1, L 10, L 36a and Fleming agglutinate well 

 each other's homologues and also the strains L 45, Rosenhain 

 and L 1a, but do not agglutinate Lister 3 or the other strains. 



The serum B.S. 6 agglutinates almost exclusively its own 

 strain and L 1a. 



There are, thus, at least three antigenic components among 

 these twelve strains, that predominant in Lister 3 which I have 

 called " I," that common to Self 1, L 10, L 36a and Fleming 

 which I have called " II," and that predominant in B.S. 6 and 

 L 1a which I have called "'III.'" 



* 17680 



D 



