PRACTICAL PHASES OF MENTAL FATIGUE. 511 



have wandered away from the Jewish race and have not affected the 

 more conservative remnant. 



The significance of this result for the science of anthropology 

 can not be overrated. The great question of the science is that 

 expressed by Dr. Galton as " the struggle between Nature and nur- 

 ture " the difference that social influences can produce on men of 

 the same race. Jews afford the science almost the sole instance in 

 which this problem can be studied in its least complex form. My 

 own investigations have shown that social environment has a direct 

 influence on such anthropometrical data as height and breathing ca- 

 pacity. The Jews of the West End of London, though of the same 

 race as those of the East End, are superior in height and other exter- 

 nal qualities, and this superiority can thus be shown to be due en- 

 tirely to nurture. Similarly, if the argument I have previously 

 adduced is correct, the brachycephalism of the Jew is a proof that 

 intellectual development produces broad heads, and that, roughly 

 speaking, the cephalic index is a key to intellectual capacity. I 

 should rather reverse Professor Ripley's main contentions : breadth 

 of skull is not a criterion of race, but of intellectual development; 

 whereas features, which are not directly influenced by social or in- 

 tellectual characteristics, are the true index to racial purity. 



SOME PKACTICAL PHASES OF MENTAL FATIGUE. 



BY PROF. M. V. O'SHEA. 

 I. 



MODERN studies in neurology have contributed much to our 

 knowledge of the function of the nervous system as a whole 

 and of its several parts, and also of the relation of psychical activity 

 to cerebral conditions and processes. The architecture of the neu- 

 ral mechanism delineated by these investigations is not only inter- 

 esting in itself on account of the marvelous unity of things appar- 

 ently diverse, but it is at the same time suggestive respecting its 

 office as the physical instrument through which mind must express 

 itself in this world. Psychologists now quite generally conceive of a 

 living being, human or otherwise, as a reacting organism, receiving 

 impressions from its environment and responding to them in some 

 characteristic manner. To be fitted for this office an individual must 

 be provided with appliances alike for the reception of stimulations 

 and for their transformation into incitements to muscular activity. 

 In the human species Nature has ordained that action need not fol- 

 low immediately and inevitably upon any sense stimulus; fortu- 

 nately, it may be deferred, so that when it does finally occur it 



