Source of Carbon and Nitrogen in Plants and Animals. 367 



portant ends ; and that if the chemical theory be capable (as few, I believe, 

 have attempted to deny") of accounting for this as well as the other pro- 

 ducts which proceed from an eruption, it ought to be adopted provision- 

 ;rily, as explaining the internal heat of the globe, in preference at least 

 to that one, which considers the latter merely as the remnant of the 

 incandescent condition, which the earth is supposed once to have pos- 

 sessed, but which leaves out of the consideration altogether the chemical 

 phenomena of a volcano, as unworthy of attention. 



I ought to apologize, perhaps, for indulging in such speculations on 

 an occasion like the present ; but the subject of volcanos will not appear 

 altogether irrelevant to that of agriculture, when I remind you that, from 

 the products of subterranean fire, many parts of the surface of our globe 

 seem to derive the fertility for which they are remarkable. All of you 

 recollect the luxuriance attributed to the lands of Campania, the " Vicina 

 Vescvo arva jugo," which in Pliny's time bore Ihree crops in the year, 

 being sown once with panic and twice with wheat, and yet, when allow- 

 ed to rest betwixt crops, produced spontaneously roses more fragrant 

 than those which resulted from cultivation in other places — " unde vulgo 

 dictum," says Pliny, " plus apud Campanos unguenti, quam apud csete- 

 ros olci fieri." 



Nor has this land, like much of that which is found in the newly settled 

 parts of America, lost its fertility by continued cropping, but at the 

 present day, as of old, stands distinguished even in that highly favoured 

 region for the abundant returns which it yields to the husbandman. 

 " Quantum autcm universas terras campus Campanus antecedit, tan turn 

 ipsum pars ejus, quae Laborefe vocantur, quern Pblegneum Grasci appel- 

 lant." 



'' Yet the farms and villages," says Liebig, "are situated from eighteen 

 to twenty-four miles asunder, and as there are no roads between them, 

 there can be no transportation of manure." He therefore attributes the 

 permanent fertility of the soil around Naples to the alkali present in the 

 volcanic materials of which it is made up ; but all felspathic rocks are 

 charged with the same ingredient, and some of them surrender it as 

 readily to the agents of decomposition ; nor, as we have seen, is alkaline 

 matter alone sufficient to supply plants with all the nourishment they 

 require. May not, therefore, the slow disengagement of ammoniacal 

 salts, as well as of carbonic acid from crevices in the mountain, likewise 

 have their share in fertilizing the ground ? These, by furnishing nitrogen 



* It was only since this lecture was in the press, that I became acquainted with 

 a memoir by rrofessor Bischof, of Bonn, in Jameson's Journal for January 1841, 

 entitled. " Reasons against the Chemical Theory of Volcanos." A more extended 

 diacOESion, however, on this subject, would be out of character with the design of 

 the present lectures ; and, as the Professor proposes to offer some further remarks 

 in a future number of the same Journal, I shall abstain from all attempt to reply 

 to his objections, until the whole of them have been put before the public. 



