76 PSYCHOLOGY. combinations of movement and impression the co-operation of the hemispheres is necessary from the start. Even in birds and dogs the power of eating properly is lost when the frontal lobes are cut off.* The plain truth is that neither in man nor beast are the hemispheres the virgin organs which our scheme called them. So far from being unorganized at birth, they must have native tendencies to reaction of a determinate sort.f These are the tendencies which we know as emotions and instincts, and which we must study with some detail in later chapters of this book. Both instincts and emotions are reac- tions upon special sorts of objects of perception ; they de- pend on the hemispheres ; and they are in the first instance reflex, that is, they take place the first time the exciting ob- ject is met, are accompanied by no forethought or delibera- tion, and are irresistible. But they are modifiable to a certain extent by experience, and on later occasions of meeting the exciting object, the instincts especially have less of the blind impulsive character which they had at first. All this will be explained at some length in Chajiter XXIV. Meanwhile we can say that the multiplicity of emo- tional and instinctive reactions in man, together with his extensive associative power, permit of extensive recouplings of the original sensory and motor partners. The conse- qv£nces of one instinctive reaction often prove to be the inciters of an opposite reaction, and being suggested on later occasions by the original object, may then suppress the first reaction altogether, just as in the case of the child and the flame. For this education the hemispheres do not need
- Goltz : Pfluger's Archiv, vol. 43, p. 447 ; Schrader : ibid. vol. 44, p.
219 if. It is possible that this symptom may be an effect of traumatic inhibition, however. f A few years ago one of the strongest arguments for the theory that the hemispheres are purely supernumerary was Soltmann's often-quoted observation that in new-born puppies the motor zone of the cortex is not excitable by electricity and only becomes so in the course of a fortnight, presumably after the experiences of the lower centres have educated it to motor duties. Paneth's later observations, however, seem to show that Soltmann may have been misled through overnarcotizing his victims (Pfluger's Archiv, vol. 37, p. 202). In the Neurologisches Centralblatt for 1889, p. 513, Bechterew returns to the subject on Soltmann's side with- out, however, noticing Paneth's work.
