160 BIOLOGY OP PLANTS. 



the greater is the proportion of gluten which they contain. Now 

 animal manures derive their special efficacy from the ammonia 

 they produce ; and it is found, that the proportion of gluten 

 depends upon the capacity of the manure to form it. Thus, 

 putrid urine and human excrements will produce much more 

 ammonia than cow-dung or vegetable matter ; and hence 

 their peculiar efficacy. The guano, which forms a stratum of 

 sixty or eighty feet in thickness in the South Sea Islands, and 

 which is composed of the excrements of sea fowls, owes its 

 fertile properties, in part, to the large quantity of ammonia 

 which it contains. This manure is an article of commerce, 

 and is placed on the barren soils of Peru, where it produces 

 the most surprising effects. It is composed mostly of urate, 

 phosphate, oxalate and carbonate of ammonia, with a few 

 earthy salts. 



Human urine contains nitrogen, in the phosphates and in 

 the urea; the latter, by putrefaction, is converted into car- 

 bonate of ammonia. Now it is well established, that human 

 urine is the most powerful manure for those vegetables vv hich 

 contain a large quantity of nitrogen. The urine of herbi- 

 ferous animals contains hippuric acid, a substance which is 

 easily decomposed into benzoic acid and ammonia. 



(3) The powerful influence of the salts of ammonia, is part- 

 ly accounted for on the supposition, that they yield nitrogen 

 to plants. The kind of influence they exert gives force to 

 this position ; for the carbonate and sulphate of ammonia in- 

 crease the quantity of vegetable products, which require the 

 largest quantity of nitrogen; that is, the gluten and vegetable 

 albumen. 



Ammonia, in cool countries, is the last product of the pu- 

 trefaction of animal bodies. A generation of a thousand mil- 

 lions of men are renewed every thirty years, and thousands of 

 animals cease to live, and are produced in a much shorter 

 period, whence the nitrogen they contained during life ? All 

 animal bodies yield ammonia to the atmosphere, hence it must 



