January 6, 1905.] 



SCIENCE. 



21 



which surround man, and in turn to pro- 

 duce a human individual more capable of 

 resistance to disturbing influences, and 

 better suited for the enjoyment of the 

 world in which he lives. 



Considering anatomical work with this 

 thought in mind, the problems which it 

 presents can be grouped according to their 

 relative value and importance. The ap- 

 proach may be made from two sides. On 

 the one hand it is, for example, extremely 

 worth while to direct years of labor to the 

 determination of the finer structure of 

 living substance, because the more closely 

 we approximate to a correct view of that 

 structure, the more readily will our anat- 

 omy and physiology run together, and the 

 clearer will be the conception of the sort 

 of structure which it will be most desirable 

 to increase for the attainment of our final 

 purpose. On the other hand, if Ave follow 

 the path from the grosser to the finer 

 anatomy, we are led to inquire whether 

 there is any one part or system of the 

 human body which at the present moment 

 is specially worthy of attention. When 

 we say that the nervous system is such a 

 part, I think that even those who are not 

 engaged in the study of it will admit that 

 there are some grounds for the statement. 

 The peculiar feature which sets the nervous 

 system apart is the fact that its enlarge- 

 ment, both in the animal series and during 

 the development of the individual, is in a 

 very special way accompanied by changes 

 in its physiological and psychological re- 

 actions. To be sure, we think of it as built 

 up fundamentally by the union of a series 

 of segments, but the relationship estab- 

 lished between these segments becomes 

 ultimately so much more important than 

 the constituent lanits that in the end we 

 find ourselves working with a single system 

 of enormous complexity rather than a 

 series of discrete units, a state of affairs 

 which is not paralleled in any other tissue. 



In addition to this, the nervous system as 

 a whole is par excellence the master sys- 

 tem of the body, and as such, the reactions 

 of the organism are very largely an expres- 

 sion of its complexity. Indeed, within 

 the different classes of vertebrates, the 

 various species may be regarded as com- 

 pound bodies composed of four funda- 

 mental tissues and a species could well be 

 defined by the quantitative relations found 

 to exist between the nervous, muscular, con- 

 nective and epithelial constituents. Work- 

 ing from this standpoint, Dubois,* the 

 Dutch anatomist, stimulated by the work 

 of Snell,f has brought forward evidence 

 for the view that when, within the same 

 order, several species of mammals similar 

 in form, but differing in size, are compared 

 with one another, the weight of the brain 

 is found to be closely correlated with the 

 extension of the body surface, and by in- 

 ference with the development of the affer- 

 ent system of neurones. This view would 

 seem to imply that in these cases there is 

 the same density of innervation of each 

 unit-area of skin ; but the correctness of 

 this inference can only be determined by 

 the careful numerical study of the afferent 

 system of the animals compared. It will 

 appear, however, that under the conditions 

 imposed, the relative weight of the brain 

 depends upon the fact that each unit-area 

 of skin, represented by the nerves which 

 supply it. calls for a correlated addition of 

 elements to the central system, and thus 

 the increase in one part is followed by 

 a corresponding increase in the other. 

 When, however, the large and small indi- 

 viduals within the same species are com- 

 pared, it is found that the increase in the 

 brain weight follows quite another law, 

 and that in this latter ease it is relatively 

 much less marked than in the former. This 



* Dubois, Archiv f. AnthropoJogie, 1808. 

 t Snell, Archiv f. Psi/chiairie u. yervenkravh- 

 heiten, 1892. 



