46 BACTERIA AND SOIL FERTILITY 



proteins. If these be broken down into their specific blocks they 

 yield nearly the same as do the higher plants. Many of these are 

 what we term complex or nucleoproteins. These proteins are 

 peculiar in that they contain large quantities of phosphoric acid. 

 Some of the bacterial proteins are extremely violent poisons and 

 are called toxins. 



The fat content of bacteria varies greatly with different species. 

 Some, as for instance the tubercle bacilli, contain considerable 

 fat. An interesting characteristic of such organisms is that they 

 are extremely hard to color, but if they are once stained (as by 

 boiling them in a strong stain) they retain the color tenaciously. 

 Not even dilute acids or alcohol will remove it. Hence, their 

 name, the "acid- fast organisms." 



Many of the common fats, such as those of beef, cotton seed, 

 and the olive, have been identified in the bacterial body. The 

 cells of the tubercle bacilli have been found to contain 26.5 per 

 cent of fat and wax in their dried substance. The nitrogen-fixing 

 organisms which live in the soil frequently store up considerable 

 quantities of fat in their cells. 



Carbohydrates are found in large quantities in the higher plants, 

 but in the case of bacteria they are conspicuous by their absence. 

 A few varieties of bacteria have been found with small quanti- 

 ties of cellulose (woody fiber), starch, glycogen (animal starch), 

 and some of the sugars. 



The quantity of ash in the bacterial cell is considerable higher 

 than it is in other plants. The same substances are found in both. 

 At times nearly three-fourths of the total ash is phosphoric acid. 

 The remainder of the ash is composed mainly of potassium, calci- 

 um, magnesium, iron, and sulfur. 



Variation in Composition of Different Parts o£ the Cell. — 

 The worker in bacteriology not only analyzes the individual cells, 

 but he determines the composition of difiFerent parts of the cell. 

 This is done by using various stains as previously suggested. The 

 outer coating of the cell, the capsule, is a sticky gum-like mass 

 which often causes the organisms to adhere together. When they 

 get into flour or yeast we have a bread which can be strung out 



