SEVENTEENTH AND EIGHTEENTH CENTURIES X4I 

 sometimes he goes so far as expressly to point out that its essence must al- 

 ways remain unknown, while, on the other hand, he is quite convinced as 

 to what it is not: it is not the immortal spirit, distinct from the body, that 

 it is officially declared to be. During a fever La Mettrie had observed how 

 the faculties of the soul within him were affected by the course of his sick- 

 ness, and in his medical practice he had remarked the same phenomenon 

 in many of his patients. By thus making the influence of the bodily functions 

 upon the intellectual life a subject for investigation and even experiment 

 La Mettrie discovered that field of research which in modern times is termed 

 psycho-physics and which has been so successfully investigated by research- 

 workers with what are, in principle, the same methods as his, though with 

 an entirely different standard of scientific criticism. La Mettrie, in fact, 

 suffered the usual fate of a pioneer in not being able to free himself from 

 the prejudices he attacked. 



His general conception of the human soul 

 He begins by accepting the old division into a vegetative, a sensitive, and 

 a rational soul; he analyses the first two and finds that their functions are 

 dependent upon those of the body, which indeed his predecessors had also 

 taken for granted. He devotes the main part of his investigation into the 

 soul to trying to discover the operation of the sensitive soul; he gives an 

 account of mental impressions and their mechanisms, in the course of which 

 he makes several striking observations, inter alia regarding the subjectivity 

 of mental perceptions. He discusses the localization of the mental functions 

 in the brain with extraordinary keen-sightedness and thence goes straight 

 over, with a somewhat daring mental jump, to ideas, which he treats — very 

 naively — as bodily entities, the grandeur of which he tries to estimate. 

 After having thus converted ideas in general into bodily phenomena, he dis- 

 cusses in connexion therewith a number of such ideas — memory, imagina- 

 tion, talent, etc. — all of which are to him likewise material, so that finally 

 there is nothing left of the rational and immortal soul that the theologians 

 have made it their mission to cherish. Thus he accumulates a mass of evi- 

 dence to show that the soul of man is fundamentally the same as that of the 

 animal; he cites examples of animal affection, gratitude, and such feelings, 

 and seeks, on the other hand, to adduce proofs that man possesses animal 

 qualities. He quotes in all seriousness a number of miraculous stories of 

 human beings who have lived like animals in the forests — probably em- 

 broidered tales of runaway lunatics — he describes the orang-utan with the 

 entirely human characteristics which were at that time ascribed to that ani- 

 mal, and hopes that it will be possible to teach it to talk by a method of 

 teaching the deaf and dumb to speak which had just been invented.^ And 



^ Why the deaf-and-dumb method should have to be used for an ape which can hear just 

 as well as a man is not explained; probably it was the novelty of the method that made it seem 

 so wonderful and induced the hope of its performing further miracles. 



