PSYCHOLOGY Ixxix 



gence begins with the appearance of the cerebral hemispheres. 

 Lamarck cites direct introspection as evidence that thought, 

 etc., takes place in the anterior region of the hemispheres. 



In dealing with the force in animals which confers upon 

 them the power of activity, Lamarck finds that it has two 

 distinct sources. In animals that have no nervous system, 

 the activating power is stated to be the subtle fluids of the 

 environment, notably caloric and electricity. These keep 

 the visible or " essential " fluids in motion, and entirely 

 dispense with any need for a nervous system to excite activity. 

 But Lamarck, influenced no doubt by Descartes, beheved 

 that all such animals were pure machines, that had no feeling, 

 and were fatally driven by their environment into one or 

 other form of activity. They had no muscular system, but 

 only possessed irritability, aroused by contact with an external 

 object. As nervous and muscular systems were acquired, 

 however, the source of their motion gradually ceased to 

 be the subtle fluids of the environment, and the nervous 

 fluid was substituted for them. 



In this second form of activity, therefore, Lamarck speaks 

 of nature as having transferred the source of motion from 

 being outside the animal, to within it. He held that there 

 was a central " reservoir " of the nervous fluid ; and that 

 when any muscles were to be acted upon, the process con- 

 sisted in the simple despatch of nervous fluid from the 

 reservoir down the nerve which led to the muscle in question. 

 When the muscular contraction was no longer desired, 

 the nervous fluid returned to the reservoir by a natural 

 recoil. 



Lamarck next had to consider by what physical processes 

 the reservoir could issue some of its fluid to the correct 

 muscles. He says it is by means of " emotions " : and that 

 the emotions again are due either to sensation or to thought, 

 to physical sensibility or to moral sensibility. We are thus 

 brought face to face with Lamarck's curious theory of the 

 physical aspects of sensation, emotion, and thought ; which 

 I shall now endeavour to indicate. 



