THE IRRIGATION AGE 



285 



undertook experiments in feeding pigs 

 and the curing of bacon and other pork 

 products, Since 1880 more than $50.000 

 was expended in this one line of effort, 

 and the best scientific talent of the 

 country was employed. Until Prof. 

 Henry's work on "Feeds and Feeding" 

 appeared, these extensive and invaluable 

 experiments were not available to our 

 people because they were printed in the 

 Danish Language. In this book of 

 Feeds and Feeding Prof. Henry has de- 

 voted a whole chapter to the Danish pig 

 feeding experiments. 



THE VALUE OF DUST. 



"If it wasn't for dust,'* said Prof. Wiley, 

 the chief chemist of the agricultural 

 department at Washington. "man would 

 have to devise a new plan of existence: 

 he would be compelled to provide him- 

 self with food by some other means than 

 agriculture. You could not have a garden 

 or a farm without dust. It would not be 

 possible for a crop to grow unless the soil 

 contained an organism capable of convert- 

 ing nitrogeneous matter into nitric acid. 

 Nitrogen is indispensable as plant, food, 

 and plants can assimilate it only when 

 presented in the form of nitric acid, com- 

 monly known as aqua-fortis. That is in- 

 capable of auto-locomotion and can be 

 distributed only through the dust which 

 falls upon the soil and upon leaves of 

 trees and plants. Hence dust is essential 

 to the pursuit of agriculture, and if it 

 wasn't being carried about constantly on 

 the breeze through the air we would 

 simply have to quit farming: animals 

 would have nothing to feed upon, and we 

 would have neither meat nor bread nor 

 vegetables. 



'*! have been spending some years," 

 continued Prof. Wiley "in the investiga- 

 tion of the agricultural value of dust, and 

 it is a very important subject. The soil is 

 continually being revived and enriched 

 from the particles that are floating about 

 in the atmosphere. They come from two 

 sources: first, atoms of the earth's surface 

 caught up by the wind and distributed 

 elsewhere, and, second, what we call 



cosmic dust that is. mineral matter of 

 meteoric origin. 



"We are getting gradually to undei-- 

 stand its quantity, its value and the im- 

 portant part it plays in agriculture. The 

 heavenly bodies are constantly shedding 

 fragments of iron and other mineral sub- 

 stances, which fall with great velocity, 

 and when they reach the atmosphere that 

 surrounds the earth are heated by friction 

 and catah fire by contact with the oxygen. 

 They are then burned to ashes and scat- 

 tered in minute and invisible atoms. . 

 Some of the larger pieces that become 

 detached from the stars reach the earth 

 without being entirely consumed. We 

 call them meteors, but the little particles 

 that premeate the air, because of this 

 perpetual and violent bombardment from 

 the stars, are composed of phosphoric 

 acid, potash and other chemicals, which 

 are absolutely essential in renewing the 

 fertility of the soil. 



"What we call terrestial dust is also of 

 great importance to agriculture. In many 

 places the soil is almost entirely com- 

 posed of particles that have been left 

 there by the winds. This is particularly 

 true of soils that are made up of volcanic 

 ashes, which are carried immense dis- 

 tances from the craters. A considerable 

 percentage of the soil on the earth's 

 surface was originally volcanic dust, 

 which has been distributed by that good 

 friend of man we call the wind. Pompeii 

 and Herculaneum illustrate the great 

 depth to which volcanic dust may reach. 

 These are called ^Eolian soils. 



"The clouds are water dust. Fog is a 

 mixture of water, coal, terrestial and 

 meteoric dust. The fogs of London might 

 be considerably reduced if the people 

 would burn hard coal. 



"The dust from the streets of cities is of 

 a composite nature and carries all sorts of 

 fragments and atoms in various stages of 

 decay. It has a high degree of agricul- 

 tural significance, because it is loaded 

 with germs of all kinds. Some of them 

 are very useful and some are injurious. 

 The effect upon the public health is not 

 injurious except where the dust carries 

 pathogenic germs that is, the germs of 

 disease. As an illustration, the sputa of a 



