48 SOURCE AND ASSIMILATION OF NIGROGEN. 



grown on a soil manured with human urine, yielded the maxi- 

 mum of gluten, namely 35*1 percent., or nearly three times the 

 quantity. Putrefied urine contains nitrogen in the forms of 

 carbonate, phosphate, and muriate of ammonia, and in no other 

 form than that of ammoniacal salts. 



Putrid urine is employed in Flanders as a manure, with the 

 best results. During the putrefaction of urine, ammoniacal salts 

 are formed in large quantity, it may be said exclusively ; for 

 under the influence of heat and moisture, urea, the most promi- 

 nent ingredient of the urine, is converted into carbonate of am- 

 monia. The barren soil on the coast of Peru is rendered fertile 

 by means of a manure called Guano, which is collected from 

 several Islands in the South Sea.* It is sufficient to add a small 

 quantity of guano to a soil consisting only of sand and clay, in 

 order to procure the richest crop of maize. The soil itself does 

 not contain the smallest particle of organic matter, and the ma- 

 nure employed is formed only of urate, phospliale, oxalate, and 

 carbonate of ammonia, together with salts, j" 



The ammonia, therefore, of the salts contained in Guano, must 

 have yielded the nitrogen to these plants. Gluten is obtained 

 from corn ; vegetable albumen from certain juices, such as from 

 the expressed juice of the grape ; vegetable casein occurs in the 

 seeds of the leguminous plants ; but although all these have dif- 

 ferent names and properties, they are identical in composition 

 with the ordinary gluten. 



It is then ammonia which yields nitrogen to the vegetable albu- 

 men, the principal azotised constituent of plants. Nitrogen is 

 not presented to wild plants in any other form capable of assimi- 

 lation. Ammonia, by its transformation, furnishes nitric acid to 

 the tobacco-plant, sunflower, Chenopodium, and Borago officinalis, 

 when they grow in a soil completely free from nitre. Nitrates 

 are necessary constituents of these plants, which thrive only 

 when ammonia is present in large quantity, and when they are 



* The guano, which forms a stratum several feet in thickness upon the 

 surface of these islands, consists of the putrid excrements of innumerable 

 ■ea fowl that remain on them during the breeding season. (See th# 

 Chapter on Manures.) 



f Boussingault, Ann. de Ch. et de Phys., lxv., p. 31 Q 



