53 



Fleming, Wollstein (4), Wilson, Hartley, Edington, Rapo- 

 port, Utheim, who used both agglutination and complement 

 fixation). 



Malone (1) tested 39 sera with the homologous strains (that 

 is lo say from the same patient) and got 32 positive and 7 negative 

 agglutinations, while 52 sera tested with a mixture of 4 heterolo- 

 gous strains gave 22 positive and 30 negative reactions. Lastly 28 

 sera were tested simultaneously with homologous and heterologous 

 strains; 23 of them gave a positive reaction with the homologous 

 strain and only 10 with the heterologous. A negative reaction with 

 the homologous strain coupled with a positive with the heterologous, 

 was never found, and the titre was always lower for heterologous 

 strains than for homologous. 



These investigations on the whole create a decided Im- 

 pression that strains of Pfeiffer's bacillus, even though they 

 are cultivated from influenza patients in the same locality, 

 cannot usually be regarded as mutually identical from 1 a sero- 

 logical standpoint. More precise information in this direction 

 can however be obtained by means of animal experiments. 



The most comprehensive investigations have been carried 

 out in America at the instigation of Park's emphatic conten- 

 tion that the mutual identity or distinction of different strains 

 of Pfeiffer's bacillus must be of great importance in the pro- 

 blem of their primary or secondary role in influenza. 



Park, Williams, & Cooper prepared rabbit serum with 20 

 chosen from 160 strains, the latter being made up of 13 strains 

 taken from autopsies and more than 60 from patients in the be- 

 ginning of the disease. They tested all the strains against all the sera 

 by simple agglutination and partly also by agglutinin absorption. 

 A certain amount of cross agglutination of one strain with the serum 

 corresponding to another strain was found, but by absorption tests 

 only 4 „pairs" could be discovered, that is to say 8 strains with 

 identical pairs. 



Valentine & Cooper in the first place examined 9 strains 

 from autopsies of influenza patients and found them all different 

 by agglutination and absorption of agglutinin. Afterwards they exami- 

 ned numerous strains cultivated from influenza early in the disease, 

 from influenza convalescents, and from the throats of healthy people, 

 — in all, 171 strains, which were tested against 25 sera, — and 

 only exceptionally found identical strains among them. Even strains 

 which were cultivated early in the disease from persons who might 

 be expected to be infected with influenza from the same source 



