ANIMAL INTELLIGENCE. 225 



to the more purely intellectual faculties, language is largely intelligible 

 to a child long before it is itself able to articulate ; but, soon after it is 

 able to articulate, the faculty of abstracting qualities and classifying 

 objects by the aid of signs begins its course of development. Thus, 

 for instance, I have lately seen a child who belongs to one of the best 

 of living observers, and who is just beginning to speak. This child 

 called a duck " quack," and by special association it also called water 

 "quack." By an appreciation of the resemblance of qualities, it next 

 extended the term " quack " to denote all birds and insects on the one 

 hand, and all fluid substances on the other. Lastly, by a still more 

 delicate appreciation of resemblance, the child eventually called all 

 coins " quack," because on the back of a French sou it had once seen 

 the representation of an eagle. Hence to this child the sign " quack," 

 from having originally had a very speciahzed meaning, became more 

 and more extended in its signification, until it now serves to designate 

 such apparently different objects as " flj'," " wine," and " shilling." And 

 as in this process we have the initiation of the logic of signs, so we have 

 in it the potentiality of the most abstract thought. Accordingly, soon 

 after a child begins to speak, we find that reason of a properly human 

 kind begins to be developed. 



Upon the whole, then, the study of infant psychology yields just 

 the kind of results which the general theory of evolution would lead us 

 to expect. But in comparing the intelligence of a j^oung child with 

 that of an adult animal we are met with this difficulty — that as the 

 bodily powers of children at so immature an age are so insufficiently 

 developed, the mind is not able, as in the case of animals, to accumu- 

 late experiences of life. In order, therefore, to obtain a fair parallel, 

 we should require a human being whose mental powers have become 

 arrested in their development at an early age, while the bodily powers 

 have continued to develop to mature age, so serving to supply the 

 aborted human intelligence with full experiences of life. Now, the 

 nearest approach that we have to these conditions is to be found in the 

 case of idiots. Accordingly, in anticipation of this lecture, I have sent 

 a table of questions to all the leading authorities on idiocy, and the 

 answers which I have obtained display a very substantial agreement. 

 Through the kindness of these gentlemen I have also been enabled to 

 examine personally a number of the patients who are under their 

 charge. In particular I have to express my obligations to Drs. Beech, 

 Crichton Browne, Langdon Down, Ireland, Maudsley, Savage, and 

 Shuttleworth. On the present occasion I can only pause to state the 

 leading facts which have been elicited by this inquiry. 



As there are all degrees of idioc}^ the object of my inquiry was to 

 determine the order in which the various mental faculties become en- 

 feebled and disappear as we descend from the higher to the lower 

 grades of imbecility. On the general theory of evolution we should 

 expect that in such a descending scale the characteristically human, or 



VOL. XIV. — 15 



