180 WHAT DOES MAN LIVE UPON? 



of albumen pre-supposes the presence of a great quantity 

 of salts of phosphoric acid. 



If we examine a healthy normal Potato, we find the 

 proportion of the nitrogenous to the unnitrogenized con- 

 stituents to average as 1 : 20 ; the proportion of salts of 

 phosphoric acid to alkaline salts is as 1:10. On the 

 other hand, freshly-manured cultivated land from phy- 

 siological reasons which it would lead me too far to 

 unfold here contains the inorganic constituents mentioned, 

 almost in the proportions of 1:2. The consequence of 

 this is, that in such soils the plant is forced to take up the 

 phosphates in larger quantities, in proportion to the alka- 

 line salts, than its nature requires, and thence a greater 

 abundance of nitrogenous matter, of albumen, is formed 

 in it, than it would contain in a normal condition. This 

 latter must infallibly render the components of the Potato, 

 which always contains a great deal of water, still more 

 prone to processes of decomposition, which then appear 

 under the most varied forms, sometimes, as in the dry-rot 

 formerly observed, principally seizing upon the starch, and 

 sometimes, as in the recent moist-rot, especially attacking 

 the cellulose. That such a disposition may in a moment 

 show itself as a ruinous disease, when external influences, 

 particularly unfavourable weather, come into operation, 

 is readily conceivable, and it stands to reason that when 

 the injurious influences which produced the seeds of the 

 disease continue, the degeneration of the Potato, and its 

 proneness to disease, must be always increasing. In such 

 cases, the theory of Liebig and Boussingault again affords 

 us a certain means of avoiding the evil. A careful con- 

 sideration of the inorganic substances soon affords us the 

 law, that it is not alone enough that the different sub- 

 stances are present in sufficient abundance in the soil, but, 



