1 8 THE CHEMICAL STRUCTURE OF BACTERIA 



Fat in bacteria appears mostly in the form of strongly light-refracting drops which 

 in the young cells are very finely distributed in great numbers in the protoplasm; with 

 increasing age, however, the drops join to form larger drops which occasionally fill the 

 whole cell interior. Analytical studies on the fat or lipoid content of bacteria have 

 been frequently conducted. From these it appears that the amount and the composi- 

 tion of the detectable fats, lipoids, and waxes vary for the several kinds of bacteria 

 and are dependent upon the conditions of growth. Thorough investigations have been 

 made most frequently with pure cultures of the tubercle bacillus, which has an un- 

 usually high fat content. In a very detailed study of this fat, four-to-five-month-old 

 glycerol-bouillon cultures of this organism were killed in the autoclave at iio° C, the 

 colonies collected on filter paper and treated with hot water until all the ingredients 

 of the nutrient medium were washed away. The material was then spread on porous 

 earthenware plates and dried at 40° C. In order to measure the fat contents of the pul- 

 verized bacterial masses, these were treated with various fat solvents in the Soxhlet 

 extraction apparatus. 



For a more precise determination of the fat of the tubercle bacillus, the same bac- 

 terial powder was extracted several times with chloroform, the different extract por- 

 tions mixed, and, after distilling off the chloroform, dried at 100° C. In this way there 

 was obtained a dark-brown, semi-solid mass with glassy wrinkles and with the odor 

 typical for tubercle bacillus cultures, like good wax from linden or flower honey. The 

 melting-point of this fatty substance was 46° C. Further chemical investigation showed 

 that the fat of the tubercle bacillus is a completely homogeneous substance which dis- 

 plays no resemblance to any other fat or wax. It seems to be rather a mixture com- 

 posed of free fatty acids, neutral fats, fatty-acid esters, and higher alcohols (lecithin, 

 cholesterin), and, in addition, a large quantity of extractives which are insoluble in 

 water and which, when heated with alkalies, disintegrate in part to form products sol- 

 uble in the water. 



The demonstration of bacterial fat is made by the usual microchemical methods. 

 Glacial acetic acid and chloralhydrate dissolve fat; Javelle water does not dissolve it; 

 osmic acid does not blacken it; iodine-potassium iodide solution colors it yellow brown. 

 Caustic potash seems to saponify the fat. The behavior of the bacterial fat toward 

 certain dyes is also notable. While the common stains (methylene blue, gentian violet, 

 and fuchsin) do not color bacterial fat, staining succeeds with Sudan III, naphtol blue, 

 and dimethylamidoazobenzol. The latter stains the fat yellow; Sudan III, red; and 

 napthtol blue, a deep blue. 



THE MINERAL DRY SUBSTANCE 



Thorough investigations have been carried out on the quantitative analysis of the 

 ingredients of the ash from many kinds of bacteria. It appears from these studies that 

 the mineral dry substance of the bacterial body always forms only a small proportion 

 of the cell substance, that it differs for the several kinds of bacteria, and that the 

 amount and nature of the mineral substance in any particular species vary with the 

 conditions of cultivation and the age of the culture.^ 



' For a review, cf. Falk, I. S.: Abslr. Bad., 7, 44. 1923. 



