290 NIGIIT-SOIL. 



for confirmation, the opinion that has beer, formed as to its crigin. 

 The islets which supply it are still tenanted, especially during the 

 night, by a multitude of sea-fowl. Nevertheless, from the calcula- 

 tions of M. de Humboldt, the excrements of these birds in the course 

 of three centuries, would not form a layer of guano of more than 

 one third of an inch in thickness ; — imagination stops short, startled, 

 in presence of the vast lapse of time which must have been neces- 

 sary to accumulate such beds of the substance as now exist, or 

 rather, as lately existed in many places ; for it is rapidly disappear- 

 ing since it has become a subject of the commercial enterprise of 

 mankind.* 



The average composition of guano must by no means be inferred 

 from the preceding analyses of picked samples : earthy matters are 

 usually present in much larger proportion than they are here stated. 

 The guano generally imported into England and France yields a 

 proportion of azote very far short of that which the 25 per cent, of 

 uric acid which has sometimes been stated to exist in this substance 

 would yield. In three trials the azote found was 0.14, 0.05, and 

 0.05 ; the mean would therefore be 0.08, which represents the quan- 

 tity of azote in pigeon's dung. 



The litter and excrement of the silkworm is used as manure in 

 the south. Analysis indicates 3 per cent, of azote in its constitution. 



Human excrements are regarded as one of the most active ma- 

 nures tliat can be employed. In countries where agriculture has 

 made real progress, this article is highly prized, and no pains are 

 spared to obtain so powerful a manure. In Flanders, feculent mat- 

 ters form the staple of an active traffic ; and in the neighborhood of 

 large towns, they form -an invaluable material for the amelioration 

 of the soil. The Chinese collect human excrements with the great- 

 est solicitude, vessels being placed for the purpose at regular dis- 

 tances along the most frequented ways. Old men, women and chil- 

 dren, are engaged in mixing them with water, which is applied in 

 the neighborhood of the plants in cultivation.! The fresh excrement 

 is occasionally worked up with clay, and formed into bricks, which 

 are pulverized when dry, and the powder is applied as a top-dress- 

 ing. One of the advantages resulting from the almost exclusive 

 use of this manure in China is this, that the fields seem to grow 

 nothing but the plant which is the object of solicitude with the 

 farmer ; it is there extremely difficult to meet with a weed. The 

 quality of feculent matter as a manure depends much on the nature 

 and abundance of the food consumed by those who furnish it. M.: 

 d'Arcet relates a curious anecdote in connection with this fact : a 

 farmer had purchased the produce of the cabinet of one of the most 



* Dr. John Davy, all whose scientific researches equal in accuracy the brilHant in 

 vestigations of his illustrious brother, has lately turned his attention to this subject: 

 he finds that we have collections of guano in Great Britain that are really not to ba 

 despised in some cases. The surface of the ground under old-established rookenes is 

 a true guano bed ; and removed and used as manure in the open field, produces most 

 excellent effects. See Dr. Davy's paper in Ed. Lend, and Dub. PhUos. Mag. OcU 1, 

 1844.— Eno. Ed. 



t Jollen, Annates de Chimie, vol. Ui. p. 65» Sd serlM 



