Because in nature all can be related to attraction 

 and repulsion, and both of these primary actions 

 originate from the same force, it seems to me, if I 

 may express my opinion, that in all nature only one 

 single force exists, namely the force of attraction 

 and repulsion . . . and there are not many forces, 

 but only one force. ($ 124, pp. 69 - 70) 



Coming to the animal functions, the study of which 

 constitutes the second part of the work, Wolff remarked that 

 his opinions have a less conclusive character. First of all 

 he drew attention to animal functions which are effected by 

 stimulation of the nerve substance and muscular action and 

 which, at first glance, are promoted by special forces: the 

 first is sensitivity, and the second is irritability. "Both 

 of these forces should be completely distinctive and distin- 

 guishable from the essential forces of plant substance; they 

 must constitute the essential force of the animal substance, 

 i.e. on which all the animal functions depend" ($ 137, p. 77). 

 From the analysis of these features, Wolff formulated a 

 cautious conclusion that a relationship exists between 

 irritability and the repulsive force 138) , and he discussed 

 the initiating cause of irritability as identical to the 

 essential repulsive force C$ 141, p. 79). CSigismund) 

 Kohlreuter carried out investigations based on this opinion, 

 which he described in an article sent to the Petersburg 

 Academy of Science. (28) 



Wolff concluded from these data that "It is more than 

 evident that irritability is inherent in the plant substance 

 in general, as in the animal, and that irritability by any 

 means does not represent the essential force of only the 

 animal substance" C$ 150, p. 85). From this he drew the 

 conclusion of the single nature of the essential force in 

 plants and animals; it is distinguished only by a different 

 animation effect (5 152, p.. 86). The analogy allowed Wolff 

 to think that irritability is based on the force of repulsion, 

 as sensitivity is on attractive force. 



The concluding paragraph begins with the statement: 

 "Considering that the essential force of the plant and animal 

 substance is inherent to these substances, no one will 

 doubt that the initial existence of the force itself has 



112 



