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circle of the culture of Pfeiffer's bacillus in fig. 9 apparently absorbs 

 all the growth-promoting substance, so that none of it can escape 

 to the outermost portion of the culture. 



Whether this is really the explanation, or whether the non- 

 increase of growth in the outer circle in fig. 9 depends upon the 

 tact that the heavy growth of Pfeiffer's bacillus in the inner circle 

 inhibits the growth of the outer portion by robbing it of other 

 nutritive substances than the „V" substance, I have been unable 

 to decide. In both cases it is intelligible that the presence of the 

 culture of Pfeiffer's bacillus in the immediate vicinity of the air 

 coccus, will hinder the increase of growth at a greater distance. 

 It is more difficult to understand how the increase of growth can 

 entirely fail quite close to the coccus colonies. The most probable 

 explanation is that „V" is absorbed by the nearest portion of the 

 Pfeiffer's bacillus culture without however being able to produce an 

 increase of growth. It is quite feasible that the growth of Pfeiffer's 

 bacillus may be inhibited in the immediate neighbourhood of the 

 growth of the other bacterium. (Production of harmful substances 

 which unlike the highly diffusible „V", can only act at short range. 

 — Deprivation of nutritive substances). The combination, inhibited 

 growth near the colony and augmented growth at a greater distance 

 from it, can easily be brought about by performing the symbiosis 

 lest on agar to which glucose or some other fermentable body 

 is added as well as the haemoglobin. If Pfeiffer's bacillus is now 

 inoculated in the form of a streak and close to it an organism 

 that can ferment the sugar etc. with marked formation of acid, 

 inhibition of the growth nearest the colony of the acid-producing 

 organism will be obtained, caused by the acid, and further away, 

 increased growth, as the „V" substance has its greatest effect there. 

 I have seen this phenomenon very plainly, around Pneumococcus 

 on ascitic agar plates containing a little haemoglobin and with the 

 addition of invert-sugar. Mild degrees of inhibition of growth nearest 

 the colony are often seen in the arrangement of the experiment 

 commonly employed, for instance in several of the cultures in 

 plate I, fig. 1. Something similar might be the cause of the absent 

 symbiosis effect when the air coccus is immediately surrounded 

 by the growth of Pfeiffer's bacillus. 



With the aid of these experiences and ideas, one will tmder- 

 sland various authors' reports, that the symbiosis phenomenon is 

 „capricious" (Olsen (3)); that the increase of growth is of variable 

 extension (Davis (b)); that there can be observed inhibition of growth 

 near the colony of the foreign bacterium, with or without increase 

 in the periphery (Jochmann & Krause, Rivers & Poole, Davis 

 (6) and others); and that the effect is not so good when Pfeiffer's 

 bacillus and the other organism are intimately mixed (Davis («)). 



It might perhaps be contended that although I have found 

 that the increase of growth which takes place when Pfeiffer's ba- 

 cillus is inoculated at a distance from the other bacterium, may be 



