xii INTRODUCTION. 



naturally involved a careful study of his normal mentalisa- 

 tion, and of the whole range of phenomena exhibited by the 

 nervous system in health and disease. 



More than twenty years ago it fell to my lot to conduct 

 a series of investigations in comparative pathology, the general 

 object and result of which was to show that the lower animals 

 are subject to the same kinds of bodily disease as those which 

 affect man. At that time I had in Edinburgh occasion to 

 experiment, for instance, on the transmission of disease 

 from man to the lower animals, and from them to him ; 

 on the artificial induction of human disorders in the lower 

 animals ; and on the comparative action of poisons on the 

 human and animal systems. Latterly my studies in com- 

 parative pathology have been determined in the direction of 

 psychopathology. I was led in the first place to enquire what 

 relation madness in the lower animals bears to insanity in 

 man, the result being the conviction that the lower animals 

 are subject to the same kinds of mental disorders, producible 

 by the same causes, as in man. This enquiry formed but the 

 precursor to a much more comprehensive investigation of 

 the normal phenomena of mind throughout the animal kingdom. 



My general conclusions, as regards both normal and 

 disordered mind in the lower animals, were made public in 

 a number of papers in certain London quarterly medical 

 and other reviews and journals in 1871-72. These pub- 

 lished papers having attracted the notice of the promoters 

 of the International Scientific Series of volumes on current 

 subjects of scientific interest, I was invited to contribute to 

 that series a volume on ' Mind in the Lower Animals ; ' which 

 invitation, though at first disposed to decline on account of 

 the very limited professional leisure I could devote to a 

 systematic exposition of my enquiries and their results, with 

 the unfavourable nature for book-making of my daily avoca- 

 tions and of my provincial (country) residence, I was finally, 

 after much correspondence, induced to accept. I did not, 

 however, feel disposed to come prominently before the public 

 without a still further and more careful study of the whole 

 subject of the animal, including the human, mind, healthy 

 and diseased. In particular, feeling, with John Stuart Mill 



