VAEIOUS KINDS OF MANUEE. . 137 



ring on the soil the most lasting advantage, as from the slowness of 

 their decomposition their beneficial effects are not so readily exhausted. 

 Plants themselves, in a soluble state, would be the best manure. In 

 ordinary farmyard manure the straw is again made available for the 

 purpose of the plant. The whole crop of wheat and oats, however, 

 cannot be returned to the soil, as part must be retained for food. A 

 substitute, therefore, must be found for the portion thus taken away. 

 This contains both azotised and unazotispd matters, the former con- 

 sisting of protein compounds which supply nitrogen for the muscular 

 tissue of man and animals ; the latter of starchy, mucUaginous, and 

 saccharine matters, which furnish carbon as a material for respiration 

 and the formation of fat. The object of manuring is chiefly to increase 

 the former, and hence those manures are most valuable which contain 

 soluble nitrogenous compounds. 



The value of manures is often estimated by the quantity of 

 glutin which is produced by their application. Hermbstaedt sowed 

 equal quantities of the same wheat on equal plots of the same ground, 

 and manured them with equal weights of different manures, and from 

 100 parts of each sample of grain produced he obtaiued glutin and 

 starch in the following proportions :— 



Without manure 

 Cow dung 

 Pigeons' do. 

 Horse do. 

 Goats' do. 

 Sheep do. 

 Dried night soil 

 Dried ox blood 



Manures containing ammonia owe their excellent qualities to the 

 nitrogen which enters into their composition; hence the value of sulphate 

 of ammonia, ammoniacal liquor of gas-works, and urine. The value 

 of guano, or the droppings of sea-fowl, depends chiefly on the ammo- 

 niacal salts, and the phosphates which it contains ; thus supplying the 

 nitrogen and phosphorus requisite for the protein compounds which 

 furnish the elements for flesh and blood. The guano which is im- 

 ported is the excrement of numerous searfowl which frequent the 

 rainless shores of South America and Africa. It often contains 

 beautiful specimens of Diatoms, as Oampylodiscus, Coscinodiscus, etc. 

 The guano found in caves on the coasts of Malacca and Cochin-China 

 is the produce of frugivorous and insectivorous bats, and of a species of 

 swallow — the last being the best. ■ 



The following analyses, by Dr. Colquhoun of Glasgow, which are 

 the result of an examination of a large number of samples, give a 

 general idea of the composition of guano. The term ammoniacal 



