117 



appear that we possess a good means of obtaining a view 

 of many things which at first sight seem to be rather compli- 

 cated. 



As the central factor in the group of substances which are 

 of special importance for the growth of Pfeiffer's bacillus, 

 stands crystallised „haemoglobin u , i. e. oxyhemoglobin. There 

 will be no difference between reduced haemoglobin and oxy- 

 haemoglobin as we are working entirely under conditions where 

 the oxygen of the air has free access, Methaemoglobin, as far as 

 it has been investigated, behaves like oxyhaemoglobin. 



It has already been stated (p. 101) that crystallised haemo- 

 globin in itself is inactive or nearly so. (The possibility that 

 different products of crystallised haemoglobin even under other- 

 wise perfectly similar experimental conditions, will not always 

 prove so absolutely inactive is not excluded, since even after 

 repeated crystallisation it can not always be regarded as a 

 substance of constant constitution (Herzfeld & Klinger)). 



But agar containing crystallised haemoglobin can be made 

 active in two ways: (1) by the addition of „V", e. g. in the 

 form 1 of yeast extract. It therefore contains „X", even in con- 

 siderable amount. Crystallised haemoglobin alone produced no 

 growth even in so strong a concentration as 1 : 10, but in 

 association with yeast extract it produced growth in a dilution 

 of 1 : 2000000. (Thjotta & Avery (2)). 



(2) By heating. Olsen (3) found agar containing crystallised 

 oxyhaemoglobin or methaemoglobin inactive. But when he 

 heated the haemoglobin agar to boiling point (and filtered off 

 the precipitate produced, which however is unimportant in 

 the present case), that is to say, when he prepared Levinthal 

 agar from it, he obtained exactty the same luxuriant growth 

 as on ordinary Levinthal agar prepared with blood. In the 

 transformation of the haemoglobin caused by heating it in agar, 

 „V" is therefore liberated in large quantities, „X" being present 

 all the time. 



Good Levinthal agar contains so much „V" that further 

 addition of it is without effect. The symbiosis phenomenon 

 can therefore not take place. But if the Levinthal agar is 

 heated for long, most of the „V" substance will be destroyed. 

 As the „X' ; substance is now present in excess, bacteria, yeasts 

 etc. can exert their action . 



