FARMERS' INSTITUTES. 21 



T.hese represent some of the functions of bacteria worthy of keeping 

 in mind; especially remember that bacteria are capable both of de- 

 structive processes and constructive processes, of analytic and synthetic 

 measures. 



The foregoing will introduce us to the study of soil, which represent 

 these two processes from the bacteriological standpoint. 



The bacteria of the soil are not found most numerous at the surface, 

 but a little below. Those found near the surface are exposed to tht; 

 alternative action of the sun, moisture and dryness, cold and heat; conse- 

 quently many succumb. But a few inches below the surface the con- 

 ditions are more equalized and the bacteria are better favored. We 

 will say in this stratum the bacteria ape most numerous, but begin to 

 diminish in number as we proceed upward or downward. At the depth 

 of six or seven feet very few bacteria exist. 



The development of bacteria in the soil is dependent upon the avail- 

 able food for th(*ir growth, the moisture present, the temperature, which 

 must be suitable, and a proper reaction; that is, too much acid must not 

 exist to prevent growth. Another element enters in our progressive 

 manipulation of the soil. Materials cannot be profitably utilized to 

 check the growth of these micro-organisms without a knowledge of their 

 action. This line of investigation has been undertaken to find a means 

 of preventing the action of bacteria which tend to waste manurial value. 



A certain amount of organic matter seems essential for the growth 

 •of bacteria. In soil possessing humus in suitable quantities, the decom- 

 position or fermentation is carried on with the proper degree of in- 

 tensity, for if the soil like fine sand be used where there is only a slight 

 trace of humus, or a soil that contains too much humus, in the one case 

 there is not sufficient food for the growth of bacteria and in the other 

 there is too much, resulting in the production of fermentation products 

 detrimental to the growth of many plants. It will be guessed that I am 

 speaking of bacteria in general. The conditions under which nitrifying 

 ,and denitrifying bacteria develop will be considered a little later. 



Moisture is as essential for the development of bacteria as in the case 

 •of plants. A plant cannot sustain life without moisture. Therefore, in 

 carrying on their functio-ns, even if the nutrition of a plant is dependent 

 upon their action, bacteria are useless without sufficient moisture. Des- 

 sication kills some, but most live through ordinary dessication and grow 

 when the needed moisture is supplied. Prolonged drouth is more likely 

 to produce undesirable results than when of short duration. While it 

 is true that bacteria have a wide range of temperat\ire, yet there are few 

 bacteria which will grow satisfactorily below 60 degrees F., and as the 

 i^emperature approaches 90 degrees F. the activity becomes much more 

 manifest. This is easily discernible, for when the temperature rises the 

 gases coming from a manure heap are plainly evident; let the tempera- 

 ture go down and the fermentation becomes slower. If the cow stable 

 is considered, the fermentation of urine in hot weather will begin within 

 one hour, while in cold weather there is little to be seen for several 

 hours. From this we may conclude that temperature is one of the most 

 important factors in the development of soil bacteria. 



The reaction of the soil has no little significance at times. It is true 

 that in the change of alkalinity and acidity, the life content of the soil 

 undergoes alteration. At one moment one set of micro-organisms pre- 



