I 4 INANITION AND MALNUTRITION 



(in variable amounts) and none of which can be substituted for each other. As 

 v. Liebig puts it: 



"Ein jedes Feld enthalt ein Maximum von einem oder mehreren und ein 

 Minimum von einem oder mehreren Nahrstoffen. Mit diesem Minimum, sei 

 es Kalk, Kali, Stickstoff , Phosphorsaure, Bittererde, oder ein anderer Nahrstoff , 

 stehen die Ertrage im Verhaltniss, es regelt und bestimmt die Hohe oder Dauer 

 der Ertrage. 1st dieses Minimum z.B. Kalk oder Bittererde, so werden die 

 Ernten an Korn and Stroh, an Ruben, Kartoffeln oder Klee dieselben bleiben 

 und nicht hoher ausfallen, auch wenn man die bereits in Boden vorhandenen 

 Kalis, der Kieselsaure, Phosphorsaure, etc., urn das hundertfache vermehrt." 



Furthermore, field experiments are cited to prove that when enough of the 

 minimum constituent is added to bring up its proportion to that of the next 

 lowest constituent, further addition of the first constituent has no further favor- 

 able effect upon the yield. 



While it is impracticable to follow in detail the controversy which has fol- 

 lowed as to the validity of this law in plants ( and later as extended to animals), 

 the result may be summed up briefly in the statement that, as formulated and 

 applied by v. Liebig, the law in general remains well established. This does 

 not mean, however (as some have claimed), that no growth whatever will occur 

 in the absence of any factor essential for normal nutrition, or that growth under 

 restricted nutriment must always result in normally proportioned dwarfs, 

 growth remaining normal until the limit is reached. Numerous examples of 

 pathological development under such conditions have been cited in the foregoing 

 pages, and some instances of such were recognized by v. Liebig. 



Furthermore, this law (as strictly interpreted) must be modified by the recog- 

 nition that growth may be limited or affected by many factors other than the 

 amount of the minimum nutrient. The proportions of the other nutrients 

 present, conditions of acidity or alkalinity, and other factors (some of which 

 were elsewhere cited by v. Liebig) certainly have more or less influence in deter- 

 mining the amount, character and outcome of growth. 



Thus the question becomes largely a matter of definition. In the sense 

 intended by v. Liebig, the law still holds good in its general application to 

 fertilizers and farm crop yields. If more strictly interpreted and extended, 

 however, it certainly requires modifications. From this point of view, one must 

 agree with the critics, such as Mitscherlich ('20), to take a recent example, who 

 formulates a law of physiological relation of growth factors. He properly 

 insists that, strictly speaking, there can be no such thing as any one minimum 

 factor alone determining the amount of growth production, since the influence 

 of all growth factors together must be considered. The significance of this 

 question for animal growth will be considered in later chapters. 



