PREFACE 3 



I have not merely confined myself in the present work to setting 

 forth the conditions essential to the existence of life in the simplest 

 organisations, and the causes which have given rise to the growing 

 complexity of animal organisation from the most imperfect to the most 

 perfect of animals ; but, believing that there is some possibility of 

 recognising the physical causes of feeUng, which is possessed by so 

 many animals, I have not hesitated to take up this question also. 



I was indeed convinced that matter can never possess in itself 

 the property of feeling ; and I imagined that feehng itself is only a 

 phenomenon resulting from the workings of an orderly system capable 

 of producing it. I enquired therefore what the organic mechanism 

 might be which could give rise to this wonderful phenomenon, and I 

 believe I have discovered it. 



On marshalling together the best observations on this subject, I 

 recognised that for the production of feeling the nervous system 

 must be highly complex, though not so highly as for the phenomena 

 of intelUgence. 



Following out these observations, I have become convinced that 

 the nervous system, when it is in the extremely imperfect condition 

 characteristic of more or less primitive animals, is only adapted to 

 the excitation of muscular movements, and that it cannot at this 

 stage produce feehng. In this particular stage it consists merely of 

 ganglia, from which issue threads. It does not present any gang- 

 lionic longitudinal cord, nor any spinal cord, the anterior extremity 

 of which expands into a brain which contains the nucleus of sensations 

 and gives origin to the nerves of the special senses, or at least to some 

 of them. When the nervous system reaches this stage, the animals 

 possessing it then have the faculty of feeling. 



Finally, I endeavoured to determine the mechanism by which 

 a sensation was achieved ; and I have shown that nothing more 

 than a perception can be produced in an individual which has no 

 special organs, and moreover, that a sensation produces nothing 

 more than a perception whenever it is not specially remarked. 



I am in truth undecided as to whether sensation is achieved by a 

 transmission of the nervous fluid starting from the point affected, 

 or merely by a communication of movement in that fluid. The fact, 

 however, that the duration of certain sensations is dependent upon 

 that of the impressions which cause them, make me lean towards 

 the latter opinion. My observations would not have thrown any 

 satisfactory light upon the subjects treated, if I had not recognised 

 and been able to prove that feeling and irritabiUty are two very different 

 organic phenomena. They have by no means a common origin, as 

 has been supposed ; the former of these phenomena constitutes a 



