GROWTH FACTORS 105 



amino-acid has been shown to be necessary for the initia- 

 tion of gro\\i:h of many strains of Streptococcus, Lacto- 

 bacillus, Diplococcus pneumonice, and B. anthracis. The 

 organisms appear to be able to synthesise adequate 

 quantities of ghitamine once growth has commenced. 

 For some organisms it can be replaced by considerably 

 larger amounts of glutamic acid. 



Haematin. — ^It has been established that haematin is 

 the X-factor required by members of the genus Hcenio- 

 philus. It can be replaced by certain inorganic iron 

 compounds which have oxidase or catalase activity. It 

 is, apparently, only necessary for the aerobic gro^vth of 

 these organisms, since anaerobically they can grow in 

 its absence. It is highly probable that haematin, or the 

 other iron compounds, are necessary for the synthesis 

 of the cytochrome system which plays an important 

 part in bacterial respiration (see Chapter XII). 



CHOH 



CHOH CHOH. 

 Me^o-Inositol. — I I This substance is 



CHOH CHOH 



CHOH 

 essential for the growth of yeasts of the genus 

 Saccharomyces . It is noteworthy that it is required in 

 amounts considerably larger than for the majority of 

 growi^h factors, milligrams rather than micrograms being 

 needed. Its function is still unknown although Eastcott, 

 who isolated it from bios, states that it is stored unchanged 

 in the yeast cell. In animal metabolism it can prevent 

 the development of " fatty liver " which normally arises 

 when there is an excess of cholesterol in the diet. Inositol 

 occurs as the phosphoric ester in the phj^in of wheat 

 germ, which interferes with the normal metabolism of 

 calcium in bone formation. 



