OF THE NITROGEN OF PLANTS. 81 



3*33 per .cent. Such great differences must be 

 owing to some cause, and this we find in the different 

 methods of cultivation. An increase of animal manure 

 gives rise not only to an increase in the number of 

 seeds, but also to a most remarkable difference in 

 the proportion of the gluten which they contain. 



Animal manure, as we shall afterwards show, acts 

 only by the formation of ammonia. One hundred 

 parts of wheat grown on a soil manured with cow- 

 dung (a manure containing the smallest quantity of 

 nitrogen), afforded only 11*95 parts of gluten, and 

 64*34 parts of amylin, or starch ; whilst the same 

 quantity, grown on a soil manured with human urine, 

 yielded the maximum of gluten, namely 35*1 per 

 cent. Putrified urine contains nitrogen in the forms 

 of carbonate, phosphate, and lactate 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 putre- 

 faction 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 pro- 

 minent ingredient of the urine, is converted into 

 carbonate of ammonia. The barren soil on the 

 coast of Peru is rendered fertile by means of a manure 

 called Guano, which is collected from several islands 

 on the South Sea.* It is sufficient to add a small 



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

 surface of these islands, consists of the putrid excrements of innumera- 

 ble sea-fowl that remain on them during the breeding season. 



G 



