Agricultural Chemistry. 291 



the period of the publication of my book, that the fertility of 

 soils and the effect of manure depended exclusively on the 

 presence in them, and on the amount, of humus or of organic 

 substances. 



" The effects of organic manure are wonderful and incompre- 

 hensible," says Schwerz {Ilaiulhuch des Spracklischen Akerhaues, 

 vol. iii. p. 33); "this is the Gordlan knot which cannot be un- 

 loosed ; it is the limit of natural science, beyond which Isis covers 

 all with the veil of mystery." " It is the vegetable and animal 

 extracts (^Bibliotlieque Universelle, vol. xxxvi.) which determine 

 the agricultural value of the soil." 



" Plants," says Berzelius {Uaiidbuch, 1839, p. 77), " obtain 

 the material for their growth from the earth and the air, which 

 are both alike indispensable to them. The earthy part appears 

 to exert on plants no other influence except only a mechanical 

 one." 



Further (vol. viii. p. 423) : " Lime serves, partly as a stimulant, 

 partly as a chemical agent, by which the constituents of the 

 arable soil or mould are rendered soluble in v/ater : hence we 

 cannot call liming a manure. Another influence of liming or of 

 the alkalies in ashes, consists in this, that by their agency the 

 organic constituents of the soil are more rapidly converted into 

 humus. It is not known in what way gypsum acts in producing 

 the good effects which experience shows it to produce." Further 

 (vol. vi. p. 101) : " We have seen, from what has been said, how 

 plants assimilate carbon and oxygen ; but we have not found 

 whence they procure the hydrogen, or the nitrogen, which certain 

 parts of plants contain in notable proportion." {Berzelius.) 



According to these doctrines, prevalent up to 1840, and 

 founded by De Saussure and Sprengel, vegetable and animal life 

 depended on the circulation of organic matter, formerly endowed 

 with vitality. When all the remains of dead plants and animals 

 in cultivated land had been set in motion, brought into the cir- 

 culation, and in this way rendered available, an increase of pro- 

 duce by cultivation, beyond this limit, was no longer possible, 

 nor an increase of the population conceivable. JNly researches 

 on the processes of putrefaction and decay (whicli form the 

 second part of my book), and on humus, had in the mean time 

 led me to another and a totally different view, which may be thus 

 expressed : 



The increase of organic life is unlimited ;* all the constituents 

 of the food of plants are inorganic (or mineral) substances. 



" A beautiful connexion subsists between the organic and inorganic 



* Of course, tlie writer means " save by the extent of land on tlie globe capable 

 of supporting vegetation." We are still very far from this limit. — W. G. 



u2 



