188 



of the strains to agglutinin do not seem to be present. This 

 follows from the fact that the strength of the heterologous 

 agglutination of each serum converges towards the homologous 

 agglutination as a maximum. Only exceptionally are the he- 

 terologous reactions observed to be stronger than the ho- 

 mologous (H 345 and H 348 with serum Me la; I 5 and H 299 

 with serum H 34). If there were great differences in agglutina- 

 bility between the various strains we should expect more irregu- 

 larity. Since the serum corresponding to a strain A does not 

 always agglutinate a strain B to the same extent as the serum 

 corresponding to B, agglutinates A, we cannot regard the 

 strength of the heterologous agglutination in any particular 

 case as an accurate measure of „agglutinative" relationship of 

 the strains. But if we take a large number of reactions into 

 account whereby chance irregularities will to a great extent 

 be eliminated, there seems to be a good deal of justification 

 for such a view (see also p. 193). 



In the following description of a number of agglutinin ab- 

 sorption experiments certain symbols are used for the sake of 

 brevity: (1) S x -f- Y, signifies, a simple agglutination lest with 

 serum corresponding to strain X against strain Y; (2) Sx, Z -f- Y 

 signifies, absorption test with strain Z and S x followed by aggluti- 

 nation with the ^absorbed" S x against strain Y. The concentrations 

 of serum and culture can be added in parenthesis. 



It was of particular interest to determine whether the 

 strains which were derived from influenzal pneumonia 

 in the same epidemic, were the same or different serologi- 

 cally. If Pfeiffer's bacillus is the primary influenza organism 

 wc should certainly expect such strains to be identical with 

 one another. 



At the time when the technique of the agglutination experi- 

 ments was worked out only two of such strains from the epi- 

 demic 1918—19 were available. But the epidemic in the be- 

 ginning of 1920 afforded utilisable though limited material, 

 Pfeiffer's bacillus being cultivated from 6 autopsies on cases 

 of influenzal pneumonia. As appears from the table, 5 of these 

 were used for the preparation of serum (I 33, 34, 35, 36, 37). 

 All these sera were tested against all the 6 strains in a special 

 agglutination experiment with the following result. 



