134 Brain : 



vert the affirmative view. Not a few of those whom we 

 know to be best equipped for forming an opinion on this 

 subject, appear to hold negative views, to wit, that the 

 human organism has long ago reached its type limits, 

 limits which under the most favorable conditions it could 

 not escape ; in short, that the human type, anatomically 

 and physiologically, is now " fixed " ; that improved con- 

 ditions will but cause it to vary within certain unsurpass- 

 able bounds ; that man will remain a man henceforward, 

 under whatever stress of evolution, continued even for 

 many thousands of years, or forever. 



When we examine the subject historically, there is 

 much to confirm the above view. Apparently the human 

 organism was as perfect four thousand years ago as at 

 present, and differed in no typical features or essentials. 

 There seems to have been no change to indicate physical 

 evolution within the historic period. 



From a histological point of view, too, there is little to 

 indicate even the most slowly-progressive development in 

 most of the tissues of the body ; for example, the osseous, 

 muscular, connective, cartilagenous, and epithelial tissues. 

 The cells of these tissues pass through a well-defined cycle 

 of growth, and give rise to a series of growth products 

 which vary, indeed, from youth to age, but show no secular 

 change from generation to generation. 



Moreover, the bone, muscle, cartilage, and other tissue 

 cells of man resemble very closely those of the lower grade 



