CHEMICAL STRUCTURE OF ACID-FAST BACILLI 



409 



291-3), and the conclusion reached that no satisfactory evidence had been brought forward 

 to prove the existence of such forms. The more recent findings of Soltys and Taylor 

 (1944) support this conclusion ; and there seems no justification for considering at length 

 the significance of observations that were almost certainly the result of faulty technique. 



Chemical Structure of Acid-fast Bacilli. — Largely owing to the work of Anderson 

 and his colleagues (1927 et seq.) at Yale University, valuable information has been 

 obtained in recent years on the chemical structure of the mycobacteria. Large 

 quantities of bacilli of different types, grown on Long's (1926) synthetic medium, 

 were extracted with a mixture of alcohol and ether, and the resulting extract was 

 treated with chloroform and with acetone. In this way the lipoid material was 

 separated into three fractions, consisting of glycerides, phosphatides, and wax. 

 The alcohol-ether extract also contained a considerable amount of polysaccharide, 

 and some basic compounds that could be precipitated by HgClj and by pliospho- 

 tungstic acid. The results of the fractionations are given in Table 25. 



TABLE 25 



Percentage Fractions of Lfpoid and other Material isolated from Alcohol-Ether 

 AND Chloroform Extracts of Acid-fast Bacilli (Chargaff, Pangborn, and Anderson 

 1931). 



It will be observed that the total lipin content was highest in the human type 

 of bacillus and lowest in the saprophytic acid-fast bacillus. The polysaccharide 

 content, on the other hand, was arranged in the reverse order. Further analysis 

 showed that the phospholipins contained saturated and unsaturated fatty acids 

 and glycerophosphoric acid ; moreover, on hydrolysis they yielded large amounts 

 of water-soluble carbohydrates, of which mannose and inositol seemed to be the 

 two most important. Besides palmitic, linoleic, and linolenic acids, there were 

 two fatty acids of special interest. One, which was optically active and isomeric 

 with cerotic acid, was termed phthioic acid ; the other, which was optically inactive 

 and isomeric with stearic acid, was termed tuberculostearic acid. Of the waxy 

 material, one portion was purified and found to be a white powder melting at 

 200°-205° C. ; the remainder formed a yellowish salve-like mass which was called 

 " soft wax." The purified wax yielded on hydrolysis about 56 per cent, of un- 

 saponifiable wax ; this corresponded to the higher alcohols of previous workers, 

 and proved to be acid-fast. The purified wax also contained polysaccharides which 

 on hydrolysis yielded a number of sugars including mannose, (Z-arabinose, and 

 galactose (see also Gough 1932). The " soft wax " appeared to be a complex 

 glyceride. From the acetone-soluble fat of the human tubercle bacillus a yellow 

 pigment was isolated. This pigment, to which the name phthiocol has been given, 

 is one of the hydroxynaphthaquinones, and is the oxidant of a reversible oxidation- 



