WHERE AND HOW WE REMEMBER. 609 



to one another has a more practicable object than the mere gratifica- 

 tion of scientific curiosity ; it is a knowledge upon which the happi- 

 ness and prosperity, or the reverse, of millions of our fellow-creatures 

 may depend. 



WHERE AND HOW WE EEMEMBER. 



By M. ALLEN STAEE, M. D. 



IF you examine the brain of a dog, or an ape, or a man, you will 

 see that it is made up of two kinds of substance, gray and white. 

 The gray substance, which is formed of round bodies of nervous 

 matter called nerve-cells, is spread out in a thin layer over the entire 

 surface of the brain. The white substance constitutes the center 

 and body of the organ, and consists of white threads or nerve-fibers 

 which pass in various directions through the brain and end in the cells 

 of the gray matter. It is the office of the white fibers to convey mes- 

 sages ; it is the office of the gray cells to dispatch them, or to receive 

 and register them. 



If a brain be properly torn apart, it can be shown that many of the 

 white threads are collected into bundles. These bundles, each of 

 which contains many thousand threads, can be separated from one 

 another and followed to their terminations. It will then be found 

 that each bundle, or tract, as it is called, connects some one organ of 

 the body with some one region of the gray matter on the surface of 

 the brain. For example, one tract joins the muscles of one half of 

 the body with the lateral part of the opposite half of the brain ; an- 

 other ascends from the surface of the body, being made up of many 

 fibers, each of which comes from one little area of skin, and this tract 

 ends in the surface of the brain just behind the first one ; another 

 bundle comes from the eye and goes to the posterior part of the brain. 

 So too the ear, the nose, the tongue, send in their bundles, and each of 

 these goes to a definite and separate region of the surface. And thus, 

 as every part of the body is connected by its own tract with its own 

 part of the gray matter, we can imagine upon the surface of the brain 

 a map of the entire body laid out, and can say, as Meynert does, that 

 the surface of the body is projected upon the surface of the brain. 



Each of the little white threads, like an electric wire in a cable, is 

 insulated from every other by a sheath. It is therefore impossible for 

 a message sent from one end of the thread to leave it ; the message 

 must go to the other end of the thread. Therefore, an irritation set 

 up in any organ of the body is always transmitted to that part of the 

 brain with which the organ is joined, and can not reach any other part 

 directly, although it may do so indirectly, by means of association 

 fibers which join the different regions with one another. The anat- 



TOL. XXT. — 39 



