72 THE GROWTH OF THE BRAIN. 



trunk, and that these latter more nearly follow the body- 

 weight, though in the case of all, except the left lung, 

 they fail to keep pace with it. Further, the acceleration 

 of growth at puberty appears earlier in the female, 

 and the percentage value of the viscera is greater. 

 Owing to the smaller development of the muscular 

 system in the female, this percentage relation is 

 intelligible. 



By way of criticism, it must be admitted that the 

 original observations used in forming these tables were 

 not homogeneous, and that for the most part the 

 observations were made on persons belonging to the least 

 favoured social classes. Further, that in view of the 

 period covered, the number of observations for each 

 organ is by no means large ; yet, despite these evident 

 deficiencies, there is reason to believe that the pecu- 

 liarities here noted have a general significance. 



Passing next to the examination -of the increase in 

 weight and size of the organs, as dependent on changes 

 in their constituent elements, it will be necessary first to 

 inquire whether, with the enlargement of the whole 

 organ during this interval, the constituent elements 

 increase in size only or in . number also. For this 

 inquiry the two methods of enlargement should be 

 clearly understood. In describing abnormal growths, 

 the pathologists employ the term hypertrophy, with the 

 connotation that the enlargement thus designated is due 

 solely to the increase in the size of the elements already 

 formed. On the other hand, the term hyperplasia is 

 used to indicate enlargement dependent on the formation 

 of new cell elements. These terms are also convenient 

 in distinguishing the two modes of normal growth. 

 Taking the elementary tissues as previously enumerated, 

 it is found that after birth the epithelial tissues in 

 various localities are being continuously renewed though 



