104 The Mechanistic Conception of Life 



differences in the forms of organs. In order to understand 

 this we must bear in mind that the processes of growth must 

 necessarily be different for different organs, as for example in 

 the formation of a root, and the formation of a stem. As 

 growth is a process in which energy is used up in overcoming 

 the resistance to growth, differences of growth can only be 

 determined either by differences in the amount of energy set free 

 in the growing organ or by differences in resistance. Differ- 

 ences in the energy must be the outcome of differences in the 

 chemical processes which determine growth. Therefore we are 

 led to the idea that differences in the forms of different organs 

 must be determined by differences in their chemical constitu- 

 tion, or, if the chemical constitutions be similar, by differences 

 in resistance to growth. That organs which differ in shape 

 are very often chemically different is a well-known fact. The 

 formation of urea in the liver and the synthesis of hippuric 

 acid by the kidneys are the consequences of chemical differences. 



In this way we are led through the mechanics of growth to a 

 conclusion which forms the nucleus of Sachs's theory of organi- 

 zation, namely, 'Hhat differences in the form of organs are 

 accompanied by differences in their chemical constitution, and 

 that according to the principles of science we have to derive the 

 former from the latter." According to Sachs there are at least 

 as many ''spezifische Bildungsstoffe " in a plant as there are 

 different organs.^ 



2. In adopting the theory of Sachs and applying it to animal 

 morphology, we must avoid a mistake very often made even 

 in the case of good theories, namely, the endeavor to explain 

 special cases which are complicated by unknown conditions. 

 Huyghens explained by his theory of light the phenomena of 

 refraction, but he could not and did not attempt to explain the 

 sensations of color. For these phenomena the wave theory of 



1 J. Sachs, Stoff und Form der Pflanzenorgane, Gesammelte Abhandlungen, 

 II, 1893. 



