CHAPTER V 



THE CHEMISTRY OF BACTERIA 



History teaches that it is the microbe and not the bullet which 

 digs the soldier's grave. Man slew his millions, but tuberculosis, 

 pneumonia, and influenza slew their tens of millions during the 

 great World War. The farmer with all his tools for tillage 

 changes only the physical nature of his soil, but the microbe 

 changes its actual chemical composition. What is the chemistry 

 of this bit of protoplasm which we must magnify hundreds of 

 times before we can see it yet which accomplishes such gigantic 

 tasks? Shall we search within it for the wonderful radium? Or 

 is the bacterial body even more mysterious than radium? Bacteria 

 are plants, and plants consist of water, carbohydrates, fats, pro- 

 teins, and ash. It is a plant which produces strychnin. Are similar 

 substances found in the microbes? The needles of the pine are 

 green; the leaves of the maple are green, yellow, or golden. Do 

 bacteria also produce pigments? If so, what is their color and 

 what are their functions? Let us see. 



How Bacteria Are Studied. — The separation of a mixture of 

 alfalfa, white clover, sweet clover, and crimson clover seed may 

 present an insurmountable diiEculty to the novice. But let him 

 sow this mixture thinly on a fertile soil; the mature resulting 

 plants are easily distinguished the one from the other. The seed 

 could easily be collected from separate plants and accurately la- 

 beled. The same is true of bacteria. The task of picking out 

 individual bacteria from a mixture would be too great for even 

 the trained worker, but sow them thinly in an appropriate soil 

 and the tiny groups which spring from the individual seeds are 

 so distinct that even the untrained eye instantly recognizes a differ- 

 ence. The soil on which bacteria are sown is called a cultural 

 medium (flural, cultural media). Different cultural media are 



