140 THE GROWTH OF THE BRAIN. 



and therefore do not warrant the idea that moderate 

 variation in the weight of the brain is a predisposing 

 cause to any particular form of brain affection. 



Bringing together the facts which have been included 

 in this chapter, it is plain that they contribute mainly 

 to a healthy scepticism concerning the current interpre- 

 tations of brain-weight. The most hopeful method of 

 investigation was the comparison of different classes in 

 the community, the classes being based on intellectual 

 performance. This has proved unsatisfactory, for the 

 reason that the individuals forming the several classes 

 have developed under different social conditions. It is 

 clear, therefore, that the differences in weight are not to 

 be associated with the difference in intellectual capacity, 

 until the possible influence of social conditions has been 

 excluded. The best comparison is that between the 

 criminals and the ordinary persons, since the conditions 

 were probably nearly similar in the two cases. It is 

 certainly very easy to indicate the point where the 

 mental capacities diminish because of the very small 

 size of the encephalon, but it must be remembered that 

 the very small encephala are never simply miniatures of 

 healthy brains, but are always more or less organically 

 defective; and our problem is thereby complicated 

 even in this case, where the relation between size and 

 intelligence seems so evident. It is therefore desirable 

 to discuss this question from the standpoint of the struc- 

 tural elements of the brain, in order to see whether 

 some of the confusing results which come from regard- 

 ing it en masse, may not be cleared up when the varia- 

 tions in the structural units are given a proper value. 



