3i34 Dr Daubeny's Speculations as to the 



amount of animal life, in regions winch continue in a state of nature, will 

 decrease in proportion to the increase of those brought under subjection 

 to man. 



But we have not the slightest reason to imagine such to be the case, 

 nor is there any ground for believing that plants in a wild condition are 

 unable to compete with cultivated ones, in the power of supplying them- 

 selves with those principles which are necessary for their existence ; al- 

 though it be true that man, by selecting for culture such as afford him 

 the greatest amount of nutriment, causes more nitrogen to be abstracted 

 from the air than would otherwise happen. 



But what appears to me the most decisive objection yet remains to be 

 stated. Once grant, with Liebig, that the nitrogen which plants possess 

 can only be obtained by them through the decomposition of ammonia, 

 audit will follow, that, iinless this gas be supplied from the interior of the 

 globe, the quantity of organic matter into which this principle enters as 

 a component part will be undergoing a continual diminution. 



For we know of no natural processes taking place on the surface of the 

 globe which generate ammonia, excepting those connected with animal 

 and vegetable decomposition ; whilst there are many — such as the com- 

 bustion of various organic substances — which, by resolving bodies con- 

 taining nitrogen into their constituent elements, would have diminished 

 the aggregate amount of them which might have formerly existed. 



Some compensating process, therefore, is clearly required ; and that, if 

 I mistake not, is the disengagement of ammoniacal gas from the interior of 

 the globe. Possibly, however, it may be suggested as another alterna- 

 tive, that the quantity of these two gases which would be required for 

 the subsistence of the whole vegetable and the whole animal kingdom, 

 when first called into being, and likewise all that which might be neces- 

 sary to supply the loss of ammonia occasioned by combustion, &c. 

 through all succeeding ages, might have been ready prepared in the atmo- 

 sphere prior to their creation. 



But independently of the difficulty of conceiving, in the case of am- 

 monia, by what means the particles of hydrogen and of nitrogen could 

 have been brought to combine on the surface of the globe without hav- 

 ing been previously deprived of their elastic condition, those who pro- 

 pound this hypothesis ought to be prepared to shew, that an atmosphere 

 charged with the gases in question to the extent which is assumed, would 

 not have been fatal to beings possessing an organization analogous to that 

 of the existing races. 



To confine ourselves to ammonia, Drs Turner and Christison have 

 shewn that less than T J 5 part of this gas, introduced into air, caused, in 

 ten hours, a shrivelling and drooping of the leaves of a plant, and its sub- 

 sequent death. It may be doubted, therefore, whether even ^'p part 

 would not be too powerful a dose for the continuance of the healthy 

 functions of the vegetable world, if permanently present, considering that 

 the juices of the plant, and the moisture of the earth in which it grows, 



