THE NEW FERTILIZATION. 95 



the greater portion abides, gradually changing its character 

 until none of the original characteristics remain. Its color 

 becomes dark brown; its odor ceases to be that of decaying 

 matter and becomes that of garden loam, and its reaction is 

 neutral or slightly alkaline. In its final state it is called 

 humus, and is the essential part of loam or mold as distin- 

 guished from the mere mixtures of the clay and sand. 



Where the ideal combination of all the underlying elements, 

 for any reason, fails to take place, there, of course, the ideal 

 soil is lacking. It is thus that we have localities of almost 

 pure clay and others of almost pure sand. The original con- 

 stituents of the basic rocks also determine the nature of 

 soils. On the other hand, these variations in soil formations 

 give us in different localities soils especially adapted to par- 

 ticular products, as corn in Illinois and wheat in Nebraska. 



The most important agent, however, if not in the original 

 formation of soils, certainly in the fertilization of them, is 

 a tiny creation which would have to be magnified some hun- 

 dreds of diameters before we could hope to see it with the 

 unaided eye. 



We have heard so much of destructive organisms in the air 

 and in the earth, in the food we eat and in the water we drink, 

 that popularly we are disposed to disregard the friendly and 

 helpful germs which also are of incalculable importance in the 

 economy of nature. Throughout the tissues of the human body 

 there dwells an immense population of phagocytes friendly 

 to our health and wellbeing, which, when certain destructive 

 forms appear, as for instance those causing suppuration, im- 

 mediately mobilize at the seat of attack and wage a terrible 

 warfare for the integrity of our physical domain and the driv- 

 ing out and destruction of the enemy. The pus and putrid 



