32 INTRODUCTION TO NEUROLOGY 



ceases, and the animal again settles down to rest. If this regu- 

 latory process is oft repeated another factor enters, viz., the 

 facilitation of a given adjustment by repetition. Thus arise 

 physiological habits or acquired automatisms. 



The more highly complex forms of individual modifiability 

 are termed associative memory and intelligence, and the latter 

 of these is by definition consciously performed. Whether con- 

 sciousness is present in the simpler forms of "associative memory" 

 as these are demonstrated by students of animal behavior in 

 lower animals cannot be positively determined. In the behavior 

 of lower animals there are no criteria which enable us to tell 

 whether a given act is consciously performed or not, and, there- 

 fore, the lower limits of intelligence in the animal kingdom are 

 problematical. In other words, the manifestations of variable 

 behavior form a graded series from the simple regulatory phe- 

 nomena of unicellular organisms, as illustrated above, to the 

 highest human intelligence, so far as these express themselves 

 objectively. 



In mankind, where intelligent behavior is dominant, the 

 stereotyping of the adjustments by repetition (true habit forma- 

 tion) may also take place, and in this case the acquired au- 

 tomatisms are sometimes said to arise by "lapsed intelligence," 

 that is, an act which has been consciously learned may ulti- 

 mately come to be performed mechanically and nearly or quite 

 unconsciously. Much of the process of elementary education 

 is concerned with the establishment of such habitual reactions to 

 frequently recurring situations. How far "lapsed intelligence*' 

 is represented in the so-called instincts of other animals is still 

 a debated question (see p. 301). 



Among the invertebrate animals, the insects and their allies 

 possess a bodily organization which favors the performance of 

 relatively few movements in a very perfect fashion, that is, the 

 action system is simple but highly perfected within its own range. 

 Their reflexes and instincts are very perfectly performed, but 

 the number of such reactions which the animal can make is rather 

 sharply limited and fixed by the inherited bodily structure. 

 Their behavior is dominated by the invariable and innate fac- 

 tors and they cannot readily adapt themselves to unusual condi- 

 tions. The vertebrates likewise have many elements of their 



