115 



The complete picture obtained from the experiments re- 

 ported in this chapter is as follows: 



Among the non-haemolytic, Gram-negative rods, which have 

 been cultivated on media containing dissolved haemoglobin, 

 from the mucous membranes of the air passages, the lungs, 

 pleura, and meninges of man, the negative test for growth on 

 ordinary agar affords a good limitation of a group of bac- 

 teria which also possess this character in common, that asci- 

 tic agar supports only slight growth at most and much scantier 

 than media containing dissolved haemoglobin. Both these quali- 

 ties persist practically unchanged even after years of cultivation 

 on artificial media. Characteristic individual differences between 

 the different strains as regards dependence upon haemoglobin 

 could not be discovered. 



The Symbiosis Phenomenon. 



Since Grassberger (1) in 1897 observed that Pfeiffer's ba- 

 cillus grows particularly well around colonies of Staphylococ- 

 cus innumerable investigators who have worked with it have 

 confirmed the phenomenon. It must be understood that it is 

 not a question of symbiosis in the true sense. In the first 

 place it is only the Staphylococcus that favours the growth of 

 Pfeiffer's bacillus and not vice versa; and in the second place, 

 immediate contact between the two is unnecessary. The effect 

 can make itself felt over a distance of a couple of cm. It is 

 produced therefore by a substance with a considerable power 

 of diffusion. A Staphylococcus culture can futhermore pre- 

 serve its activity after being killed by gentle healing. (Staphylo- 

 coccus has only been named as an example of a growth- 

 promoting organism; many other bacteria have exactly the 

 same action). 



For a long time „symbiosis'' featured as a somewhat iso- 

 lated phenomenon in the biology of Pfeiffer's bacillus. Latterly 

 however we have come to look upon this phenomenon in 

 its relationship to the other biological properties of this micro- 

 organism. We may imagine that 3 things are necessary for 

 the growth of Pfeiffer's bacillus. 



(1) Some salts and other substances which do not play 



