44 



BACTERIA AND SOIL FERTILITY 



It was suggested to build a huge outline on some great plain on 

 the earth's surface — possibly on one of the deserts. This gigan- 

 tic structure was to have some simple suggestive form as a circle, 

 a triangle, a "T", or an *'H". The inhabitants seeing this would 

 understand^and by a similar contrivance signal back to the earth. 

 Such methods have never been used to communicate with other 



worlds. But by sim- 

 ilar means we have 

 made the inhabitants 

 of the infinitely small 

 communicate to us 

 the secrets of their 

 hidden life. 



The shape and 

 structure of these col- 

 onies differ as widely 

 as do the plants of 

 the alfalfa and 

 clover. Hence, they 

 can be distinguished 

 one from the other. 

 Moreover, isolated 

 colonies can be seed- 

 ed into other media, 

 and in this way we can obtain pure cultures. By growing massive 

 cultures in large flasks we can obtain sufficient to analyze. Or 

 if we wish to analyze a single cell we place on it a specific dye 

 and examine it under the microscope. If it contains fat, that part 

 of the body is stained red. Another dye is added, and if starch 

 be present it will be blue. If another part turns black when dye is 

 added it contains sulfur, and so on until we have learned all the 

 substances which compose its minute body. Such methods reveal 

 the fact that bacteria are composed of water, carbohydrates, fats, 

 protein, and ash. 



Water. — Next to living matter water is the most wonderful 

 thing in the world. The ancients recognized this, and Thales 



^^ Jj |^# ^■.'; 



Fig. 22. — Colonies of bacteria on agar-agar cul- 

 tural media. 



