Licbig's Organic Chemistry applied to /Jgriculture, 57 1 



although, according to Liebig, the soil has been poisoned by un- 

 assimilable excretions. It seems as if the author never saw a field, 

 and that the bare places in it are known to him only from books on 

 rural economy, where the term " bare places" is used to imply those 

 spots where the cultivated plants do not grow, but not a bare 

 soil destitute of vegetation. In his explanation of this subject, 

 we find, p. 153, the following proposition : " Though a certain 

 quantity of carbon in the soil be sufiScient to bring many plants 

 to complete development, it is not suflftcient to provide their different 

 organs with the greatest possible supply of nourishment." Accord- 

 ing to my weak understanding, nothing is in this passage clear, 

 except its absurdity. No plant can attain more than its complete 

 development, and the quantity required to produce that effect is 

 called the maximum of nourishment, whilst a minimum implies, that 

 the nourishment is so scanty, as to be hardly sufficient to maintain 

 the life of the plant. Possibly Dr. Liebig has here confounded 

 the plant with the field, and intended to say, that even when some 

 plants in a field attain their complete development, there may 

 not be sufficient nourishment for all of them, so that the field 

 does not yield the maximum of produce. At p. 74, Dr. Liebig pro- 

 mises to prove that " all animal manure acts on vegetation only 

 by forming ammonia." But at p. 154, where he treats of manure 

 more copiously, he says, the opinion that manure acts on plants 

 by the nitrogen it contains, and that this matter is assimilated 

 by the plants for the formation of gluten, is quite void of foundation. 

 For, continues he, the quantity of nitrogen contained in animal manure 

 is so small, that it cannot be taken into account. At p. 74, he 

 himself had produced the well-known facts, which prove the increase 

 of gluten in Wheat, as soon as manure containing much nitrogen 

 (i. e. animal excrements) is employed ; and in the following pages 

 he proves beyond all doubt, that we know no means by which the 

 gluten of cultivated plants can be increased, except from animal 

 excrements, and that ** the powerful effect of this kind of manure 

 can only be ascribed to the quantity of nitrogen it contains." 

 I have no doubt that Dr. Liebig, in speaking of this matter, applies 

 the terms " animal manure" and " animal excrements," in one place 



