120 



It is however not universal that the „X" function and a 

 positive oxygen-carrying reaction go together. Thjotta & 

 Avery found banana was active in the same way as potato. 

 but it did not react with benzidin however. Perhaps Rivers 1 

 (4) egg medium (see p. 102) also does not conform! to the rule. 



Various metallic salts which are quite inactive as growth 

 factors for Pfeiffer's bacillus, can react with guaiac. Benzidin 

 is more specific for haemoglobin derivatives (Gregersen) and 

 will undoubtedly react more rarely with substances devoid of 

 the „X" function. 



It is greatly to be recommended on Olsen's (3) advice, 

 that the (guaiac or) benzidin test be carried out on every me- 

 dium', before using it in the investigations of haemoglobin- 

 ophilia. 



In order to give some idea of the symbiosis phenomenon 

 in the form' which must be considered most rational at the 

 present time, it has thus proved necessary to give a review, — 

 although a very short one — of the whole question of nu- 

 tritive substances for Pfeiffer's bacillus, a review which will 

 also serve as an introduction to that section in which the 

 technique of cultivation will be dealt with. 



Besides the already named authors, may be mentioned Can- 

 tani, Ghon & Preyss, Kalkrrenner, and Pringsheim. My own 

 experiences, which will now be related in detail, are also taken 

 into account in this review. 



One cannot work long with Pfeiffer's bacillus before the 

 augmented growth around colonies of chance contaminating 

 cocci and other kinds of bacteria, attract one's attention. Illu- 

 strations of such fortuitously arising „sym'biosis" effects will be 

 found in the work of Thomsen, Kristensen, & Thorrorg 

 (Figs. 7, 8, 9, & 13). 



As similar phenomena are usually not observed in the 

 case of other species of bacteria, I consider that this phenome- 

 non should be regarded as one of the most characteristic 

 features of Pfeiffer's bacillus and therefore ought to be included 

 in the purely routine demonstration of this organism even in 

 larg^ investigations. 



An account will now be given of my experiences concerning 



