22 INTRODUCTION TO NEUROLOGY 



This distinction between the blind working of a stereotyped 

 action system whose character is determined by the inherited 

 bodily structure, on the one hand, and individually acquired 

 variable adaptive actions (which may or may not be intelli- 

 gently performed), on the other hand, is very fundamental, and 

 we shall have occasion to return to it. Most animal activities 

 contain both of these factors, and it is often very difficult 

 to analyze a given example of behavior into its elements, 

 but the distinction is nevertheless important. Plant life is 

 characterized by the dominance of invariable types of reaction 

 which are determined by innate structure; these in their most 

 elementary forms give us, in fact, the so-called vegetative func- 

 tions. These same functions predominate in the lowest animals 

 also; but in the higher animals, as we shall see, there are two 

 rather distinct lines of evolutionary advance. In one line the 

 innate stereotyped functions are very highly specialized, leading 

 up to a complex instinctive mode of life; in the other line these 

 functions are subordinated to a higher development of the indi- 

 vidually acquired variable functions, leading up to the intelli- 

 gence and docility of the higher mammals, including the human 

 race. 



The distinction between plants and animals is very difficult 

 to draw and, in fact, there are numerous groups of organisms 

 which at the present time occupy an ambiguous position, such 

 as the slime molds. The botanists claim them and call them 

 Myxomycetes; the zoologists also describe them under the name 

 Mycetozoa; still other naturalists frankly give up the problem 

 and assign them to an intermediate kingdom, neither vegetable 

 nor animal, which they call the Protista. As children we prob- 

 ably considered the chief distinction between plants and ani- 

 mals to be the ability of the latter to move freely about; but one 

 of the first lessons in our elementary biology was the correction 

 of this notion by the study of sedentary animals and motile 

 plants. Nevertheless, I fancy that in the broad view the child- 

 ish idea has the root of the matter in it. The plants and seden- 

 tary animals may have their vegetative functions of internal 

 adjustment never so highly specialized and yet remain rela- 

 tively low in the biological scale because their relations with 

 the environment are necessarily limited to the small circle within 



