86 BACTERIOLOGICAL CHEMISTRY 



would be recognised. It is probable that most, if not 

 all, organisms require the various growth factors, and 

 that they differ only in their ability to synthesise one or 

 more of them. 



Organisms of the Hcemophilus group which require 

 two growth factors are probably the most highly evolved 

 of the bacteria from the nutritional standpoint. The 

 X -factor, derived from the haemoglobin of the blood, 

 may not be a generally required factor, although there 

 is some evidence that certain bacteria (for example, 

 C. xerosis and Esch. coli) may be able to synthesise it 

 from iron compounds. The F-f actor, which is also 

 present in blood, can be derived from various bacterial 

 and vegetable extracts and appears to be of much more 

 general occurrence ; even bacteria which have very simple 

 nutritional requirements produce it . The various members 

 of the influenza group of bacteria have lost the power of 

 synthesising one or other or both of these factors. 

 H. canis, for instance, has lost the capacity to produce 

 the Jl -factor and must be supplied with it, but it can 

 make its own F-factor. The hsemolj^ic influenza bacilli 

 have lost the power of synthesising the F-factor, but 

 can do without added X-factor ; whilst H. influenzce 

 itself cannot synthesise either the X- or F-factors and 

 must be supplied with both from an external source. 

 The pneumococcus, meningococcus and gonococcus also 

 belong to this highly evolved group. 



Parasitic organisms, particularly pathogenic ones, have 

 much more complex growth requirements than the sapro- 

 phjrtic organisms. It seems reasonable to assume that 

 this is because the parasites find in their host a source 

 of nearly all of their needs in a preformed condition and 

 in the course of time have lost the necessary synthetic 

 powers to build up their OAvn requirements. This differ- 

 ence of demands between saprophytic and parasitic 

 organisms is well illustrated by the acid-fast bacteria. 

 The purely saprophytic Mycobacterium phlei can grow 



