OF MANURE. 



63 



very simple manner. An unpoetical hand 

 has pointed out the cause of the wonderful 

 and apparently inexplicable healing virtues 

 of the springs in Savoy, by which the inha- 

 bitants cured their goitre ; it was shown that 

 they contain small quantities of iodine. In 

 burnt sponges used for the same purpose, 

 the same element was also detected. The 

 extraordinary efficacy of Peruvian bark was 

 found to depend on a small quantity of a 

 crystalline body existing in it, viz. quinine ; 

 and the causes of the various effects of 

 opium were detected in as many different 

 ingredients of that drug. 



Calico-printers used for a long time the 

 solid excrements of the cow, in order to 

 brighten and fasten colours on cotton goods ; 

 this material appeared quite indispensable, 

 and its action was ascribed to a latent prin- 

 ciple which it had obtained from the living 

 organism. But since its action was known 

 to depend on the phosphates contained in it, 

 it has been completely replaced by a mix- 

 ture of salts, in which the principal con- 

 stituents are the phosphates of soda and 

 lime.* 



Now all such actions depend on a definite 

 cause, by ascertaining which we place the 

 actions themselves at our command. 



It must be admitted as a principle of agri- 

 culture, that those substances which have 

 been removed from a soil must be com- 

 pletely restored to it, and whether this resto- 

 ration be effected by means of excrements, 

 ashes, or bones, is in a great measure a mat- 

 ter of indifference. A time will come when 

 fields will be manured with a solution of glass, 

 (silicate of potash,) with the ashes of burnt 

 straw, and with salts of phosphoric acid, 

 prepared in chemical manufactories, exactly 

 as at present medicines are given for fever 

 and goitre. 



There are some plants which require 

 numus, and do not restore it to the soil by 

 their excrements ; whilst others can do with- 

 out it altogether, and add humus to a soil 

 which contains it in small quantity. Hence 

 a rational system of agriculture would em- 

 ploy all the humus at command for the sup- 

 ply of the former, and not expend any of it 

 for the latter; and would in fact make use 

 of them for supplying the others with 

 humus. 



We have now considered all that is requi- 

 site in a soil, in order to furnish its plants 

 with the materials necessary for the forma- 

 tion of the woody fibre, the grain, the roots, 

 and the stem, and now proceed to the con- 

 sideration of the most important object of 

 agriculture, viz. the production of nitrogen 

 in a form capable of assimilation the pro- 

 duction, therefore, of substances containing 



* This mixture of salts is sold to calico-printers 

 in large quantities under the name of " dung sub- 

 stitute." It would be well worth experiment to 

 try its effects as a manure upon land. Its cost is 

 3d. or 4d. per pound, and is not, therefore, dearer 

 than nitrate of soda, which is now so extensively 

 used. ED. 



this element. The leaves, which nourish 

 the woody matter, the roots, from which the 

 leaves are formed, and which prepare the 

 substances for entering into the composition 

 of the fruit, and, in short, every part of the 

 organism of a plant, contain azotised matter 

 in very varying proportions, but the seeds 

 and roots are always particularly rich in 

 them. 



Let us now examine in what manner the 

 greatest possible production of substances 

 containing nitrogen can be effected. Nature, 

 by means of the atmosphere, furnishes ni- 

 trogen to a plant in quantity sufficient for 

 its normal growth. Now its growth must 

 be considered as normal, when it produces 

 a single seed capable of reproducing the 

 same plant in the following year. Such a 

 normal condition would suffice for the ex- 

 istence of plants, and prevent their extinc- 

 tion, but they do not exist for themselves 

 alone; the greater number of animals de- 

 pend on the vegetable world for food, and 

 by a wise adjustment of nature, plants have 

 the remarkable power of converting, to a 

 certain degree, all the nitrogen offered to 

 them into nutriment for animals. 



We may furnish a plant with carbonic 

 acid, and all the materials which it may re- 

 quire; we may supply it with humus in the 

 most abundant quantity; but it will not at- 

 tain complete developement unless nitrogen 

 is also afforded to it; an herb will be formed, 

 but no grain ; even sugar and starch may 

 be produced, but no gluten. 



But when we give a plant nitrogen in 

 considerable quantity, we enable it to attract 

 with greater energy from the atmosphere 

 the carbon which is necessary for its nutri- 

 tion, when that in the soil is not sufficient; 

 we afford to it a means of fixing the carbon* 

 of the atmosphere in its organism. 



We cannot ascribe much of the power 

 of the excrements of black cattle, sheep, 

 and horses, to the nitrogen which they con- 

 tain, for its quantity is too minute. But that 

 contained in the faeces of man is proportion- 

 ably much greater, although by no means 

 constant. In the faeces of the inhabitants of 

 towns, for example, who feed on animal 

 matter, there is much more of this consti- 

 tuent than in those of peasants, or of such 

 people as reside in the country. The faeces 

 of those who live principally on bread and 

 potatoes are similar in composition and pro- 

 perties to those of animals. 



All excrements have in this respect a very 

 variable and relative value. Thus those of 

 black cattle and horses are of great use on 

 soils consisting of lime and sand, which 

 contain no silicate of potash and phosphates ; 

 whilst their value is much less when applied 

 to soils formed of argillaceous earth, basalt, 

 granite, porphyry, clinkstone, and even 

 mountain-limestone, because all these con- 

 tain potash in considerable quantity. In 

 such soils human excrements are extremely 

 beneficial, and increase their fertility in a 

 remarkable degree ; they are, of course, as 



