121 



(1) the technique of demonstrating the symbiosis pheno- 

 menon: (2) the question as to how far all strains of Pfeif- 

 fer's bacillus conform' to a standard of „symbiosis"; (3) various 

 conditions relating to the mode of action of the growth- 

 promoting bacteria. 



After at first having tried different methods of performing 

 the symbiosis test, I finally evolved a definite method of pro- 

 cedure which, in its simplicity, proved itself to possess con- 

 siderable advantages over the arrangements of the test com- 

 monly employed. 



On a plate of ordinary agar containing about 1% haemo- 

 lysed blood corpuscles, Pfeiffer's bacillus is inoculated in two 

 parallel streaks at about 1 cm', distance. Between these streaks 

 a suitable species of bacterium' is inoculated at a single point 

 on the agar surface. „Symbiosis" then shows itself by the 

 presence of a very rich growth of both streaks of Pfeiffer's 

 bacillus in the vicinity of the colony of foreign bacterium, — 

 within the limit of 1 to 2 cm. from it, — while the growth 

 outside this zone of activity is quite weak (see plate I). 



This technique comprises many factors, each of which is 

 important in itself. 



Firstly it can be noted that the agar ought not be sterilised 

 at a higher temperature than 100°, as it is not always possible 

 to obtain a rich growth of Pfeiffer's bacillus on autoclaved 

 agar. In a large number of my investigations I have however 

 used agar to which ascitic fluid has been added, in which case 

 the agar could be autoclaved without detriment. 



Of greater importance is the nature and amount of the 

 „haeni'oglobin" added. It is sufficiently evident from the above 

 that we can only be certain of getting a growth round the 

 colonies of foreign bacteria (by „foreign" is meant, different 

 from' Pfeiffer's bacillus), on agar containing „haemoglobin". 

 But it is not even on every batch of „haembglobin"-agar that 

 these organisms will evince their growth-promoting action. 



It is postulated above that when both „X" and „V" are 

 present in large quantities, the further addition of one of the 

 components (no matter in what form) will have no percep- 

 tible effect. : ; : .; ; • ! \-\r\ ; if! 



It is a matter of common experience (Grassberger (2), 



HUNDESHAGEN, BROWN & ORCUTT, PrINGSHEIM, WOLF, Sk.UAA), 



