PROGRESS IN EXPERIMENTAL PSYCHOLOGY 



mass of associations as upon the inclusion of certain 

 other associations. For example, a student in solving a 

 mathematical problem must for the moment become 

 quite oblivious to the special associations that have to 

 do with geography, natural history, and the like. But 

 does histology give any clew to the way in which such 

 isolation may be effected ? 



Attempts were made to find an answer through con- 

 sideration of the very peculiar character of the blood- 

 supply in the brain. Here, as nowhere else, the ter- 

 minal twigs of the arteries are arranged in closed sys- 

 tems, not anastomosing freely with neighboring systems. 

 Clearly, then, a restricted area of the brain may, through 

 the controlling influence of the vaso-motor nerves, be 

 flushed with arterial blood, while neighboring parts re- 

 main relatively anaemic. And since vital activities un- 

 questionably depend in part upon the supply of arterial 

 blood, this peculiar arrangement of the vascular mech- 

 anism may very properly be supposed to aid in the 

 localized activities of the central nervous ganglia. But 

 this explanation left much to be desired in particular 

 when it is recalled that all higher intellection must in 

 all probability involve multitudes of widely scattered 

 centres. 



No better explanation was forth-coming, however, 

 until the year 1889, when of a sudden the mystery was 

 cleared away by a fresh discovery. Not long before 

 this the Italian histologist, Dr. Camille Golgi, had dis- 

 covered a method of impregnating hardened brain tis- 

 sues with a solution of nitrate of silver, with the result 

 of staining the nerve cells and their processes almost in- 

 finitely better than was possible by the method of Ger- 

 lach, or by any of the multiform methods that other 



