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cus „III", Coli bacillus „IV", and Bacillus faecalis alcaligenes), and 

 4 that had shown a weak effect („Diarrhoea of calves", „Ratin", 

 Coli bacillus „II", haemolytic Streptococcus ,,11"). All these were 

 tested in a symbiosis reaction with the following 9 strains of Pfeif- 

 fer's bacillus: I 5 („typical" growth, indol), I 6 („typical" growth, 

 -f- indol), Me la („typical" growth, -J- indol) H 151 („atypical" 

 growth, only weak symbiosis, indol), H 160 („typical" growth, 

 -f- indol), H 164 („typical" growth, -f- indol), H 171 („atypical" 

 growth, only weak symbiosis, indol), H 179 („atypical" growth, 

 only weak symbiosis, indol), and H 205 („atypical", that is to 

 say, yellow growth, indol). This is a very heterogeneous selec- 

 tion as regards habitat, mode of growth and biochemical characters. 



Each test was put up in duplicate at least. All the strains of 

 Pfeiffer's bacilli with the exception of H 151 and H 171 each gave 

 exactly the same grouping of the 9 bacterial strains with respect 

 to vigorous and weak growth-promoting activity. 



In the case of H 151 and H 171 the results vere rather 

 obscure, which cannot be wondered at in view of the fact that these 

 strains of Pfeiffer's bacilli, as stated, only gave a weak symbiosis 

 reaction with bacteria known to be good growth-promoting ones. 

 On repeating the test with H 151; the relative aclivity of the 

 various bacterial species agreed fairly well with that given above, 

 with the exception of the two coli strains which acted with about 

 the same intensity. The same was the case for H 171 towards 

 which the other strains behaved in the usual manner. H 151 and 

 H 171 were now tested in 6 new experiments with both coli strains. 

 The action of these was weak in every instance and therefore diffi- 

 cult to judge, but on the whole „IV" had a stronger action 

 than ,,11". 



From' this experiment we must look upon it as highly 

 probable that practically the same result would be obtained 

 whichever growth-promoting bacterium was employed, if only 

 the latter possessed pronounced activity. 



Further it has been shown, as will later be referred to, 

 in an experiment with Bacillus haemoglobinophilus canis and 

 the whooping-cough bacillus in association with a large number 

 of other species of bacteria, that in no case was there a 

 symbiosis effect. With regard to the absence of effect on ba- 

 cilli other than Pfeiffer's bacillus, the different species of bac- 

 teria therefore also agree with one another. 



It is therefore justifiable to assume that it is a matter 

 of indifference what bacterium we employ in the symbiosis 

 test if it has a marked growth-promoting power upon any 

 strain of Pfeiffer's bacillus chosen at random. 



