THE LIPOIDS OF MICRO-ORGANISMS 377 



fractions is mycolic acid ; but that from the avian 

 bacilli is different from the wax mycolic acids ; it is 

 called y-mycolic acid and on vacuum distillation gave 

 18 per cent, of a branched chain tetracosanoic acid, 

 C24H48O2. The hydroxy-acid from the leprosy bacillus is 

 leprosinic acid, which also gives a branched chain tetra- 

 cosanoic acid on pyrolysis. The unsaponifiable material 

 consists of r/-2-eicosanol and 6?-2-octadecanol. 



The chloroform soluble wax from the attenuated 

 strain of tubercle bacillus, B.C.G., is a complex mixture 

 giving a pentose polysaccharide, palmitic and cerotic 

 acids and an acid-fast Avax, C51H102OH.COOH, on 

 hydrolysis. It has been claimed that the wax content 

 of the ether extracts of the various acid-fast bacteria is 

 characteristic of the different types ; thus the lipoids of 

 human and bovine tubercle bacillus contain 60 to 70 

 per cent, of wax, those of avian and cold-blooded tubercle 

 bacilli, the leprosy bacillus and M. pJilei contain 27 to 

 30 per cent., whilst the smegma bacillus and dung bacilli 

 contain only 4 to 10 per cent. Waxes have also been 

 obtained from the diphtheria bacillus, but have not 

 been investigated chemically. 



The evidence for the presence of sterols in bacteria 

 is somewhat conflicting ; it has been claimed that 

 Azotobacter chroococcum contains ergosterol to the extent 

 of 0-1 per cent, of the fat fraction, and that sterols occur 

 in human and bovine tubercle bacilli, in the B.C.G. strain, 

 in 31. jjhlei and in Esch. coli. Cholesterol has been 

 reportecl as occurring in L. acidophilus. The majority 

 of reports, however, state that sterols are absent from 

 bacteria. On the other hand, yeasts contain large amounts 

 of ergosterol, up to 20 per cent, of the fat being quite 

 common. Yeast is the chief commercial source of ergo- 

 sterol, which is used in the mamrfacture of synthetic 

 vitaniiu-T) or calciferol. Ergosterol also appears to be 



