178 WHAT DOES MAN LIVE UPON? 



and the carrying out possible. But vegetable physiology 

 will, with good right, make an objection to this system of 

 manuring, and experience will confirm it ; namely, that 

 though the humus, as already shown, is by no means a 

 nutrient substance, yet without it, there can be no healthy 

 and strong vegetation on such soils, and they are rare, as 

 are not most propitiously mingled with clay, which may, 

 to a certain extent, replace humus. Liebig's chemical one- 

 sidedness, in this respect, will probably be mischievous to 

 those agriculturalists who cannot neutralize this fault by 

 their own thorough knowledge of Natural Science, just as 

 on the other side, the absence of a thorough study of 

 Natural Science, and crude empirical prejudice, have in these 

 later times prevented many, particularly German agricul- 

 turalists, from taking part in the improvements called 

 forth by the progress of science. Perhaps, however, an 

 event which is sad enough in itself, will give rise to an 

 earnest observation of the results of science, and will thus, 

 by producing an essential transformation of our agri- 

 cultural management, become a blessed moment in the 

 history of our cultivation. I mean the Potato Disease, 

 which in the last few years has appeared in such a 

 threatening form, that it is, indeed, calculated to awaken 

 the most indolent from their slumber, and in which we 

 have one of the best proofs of the correctness of Liebig's 

 theories. 



The phenomenon of these recent times is by no means 

 an isolated one, for, during more than one hundred years 

 has the disease shown itself in Potatoes ; and in each recur- 

 rence of its appearance, has it exhibited greater extension 

 and activity. That it is not dependant solely or essentially 

 upon meteorological influences, is shown even by the form 

 continually becoming worse ; but, in particular, by its 



