62 The Science of Life. 



velopment of the cretin, and with most successful re- 

 sults. 



We cannot follow the history; it is enough to say 

 that although much remains uncertain as to what exactly 

 the thyroid, with its internal secretion, does to the 

 blood, there is no doubt that this inconspicuous organ 

 does something essential in keeping the blood and ner- 

 vous system up to a certain standard of efficiency. 



Another characteristically modern physiological move- 

 ment has been the analysis of the nervous mechanism 

 Anal sis which determines alike the behaviour of 

 of Nervous animals and the conduct of man. This is 

 Mechanism. the supreme anc j t h e most baffling problem 

 of the physiologist, and he has moved towards its solu- 

 tion along two paths which have led him to results 

 sometimes congruent, and yet often discrepant, en- 

 couraging and yet warning him at every turn. 



One of the two paths is experimental, and among 

 those who have moved most steadily along it are 

 Ferrier, Fritsch, Hitzig, Munk, Goltz, and Horsley. 

 One of their main aim and, to some extent, achieve- 

 ments, has been the localization of certain functions in 

 certain parts of the brain, and along certain tracts of 

 the nervous system. The inquiry was begun by Willis, 

 but in the period between him and Horsley even the 

 language has changed. 



The other path is histological the attempt by mi- 

 croscopic analysis to find a way through the extraordi- 

 nary maze of cells and fibres which form the brain and 

 spinal cord. Albert von Kolliker was one of the most 

 illustrious pioneers, and even as veteran he has not 

 ceased to lead. No small part of the progress, how- 

 ever, has been due to the discovery of new methods 

 which we especially associate with the names of the 

 Italians Golgi and Marchi, and the Spaniard Ramon y 

 Cajal. 



The cell-doctrine of Schwann and Schleiden (1838-9) 

 was not merely a morphological generalization (that all 

 Cellular organisms have a cellular structure), it was 

 Physiology. a i so a physiological theory which sought to 

 express the function of an organ in terms of the changes 



