MIND AND THE NERVOUS SYSTEM. 5 



and, if you have only profited by the instruction you have received, 

 you have a store of facts at your command that will enable you to 

 recognize heat, light, electricity, gravitation, magnetism, whenever you 

 see them manifested. When, therefore, you ask me what mind is, I 

 answer that it is a force possessing peculiar properties, and developed 

 by a substance constituting a part of the nervous organism of man 

 and other animals, and known to anatomists and physiologists as gray 

 nerve-tissue. This is similar in all essential respects, so far as its 

 terms are concerned, to the definition that you would give me of any 

 other force. Of course, it can be made more precise and extensive, 

 but no enlargement would change its character. 



The gray nerve-tissue exists in the form of aggregations of minute 

 cells in various parts of the nervous system. In man, by far the largest 

 collections are found in the brain, and especially on the outside of it, 

 covering it as the rind covers an orange, and hence called the cor- 

 tex, or the cortical substance. Besides this large mass, spread out to 

 the thickness of the twelfth of an inch or more over the exterior of 

 the brain, there ai'e masses of gray nerve-tissue in other parts, varying 

 in size from that of a walnut to that of a small pea. In this diagram 

 the situations of the masses of gray tissue existing in the brain are 

 shown. You will observe a very beautiful arrangement for increasing 

 the extent of the cortical substance without at the same time increas- 

 ing the size of the brain, and thus making it heavier than it would be 

 comfortable to carry. The surface is convoluted, and the gray matter, 

 following the convolutions, is hence doubled over and over again on 

 itself. If the cortex were spread out smoothly, like the skin on an 

 apple, it would cover a body more than four times the size of the aver- 

 age human brain. We should, then, in order to get as much mind- 

 producing substance as we have now, require heads four times the 

 volume of those that we now carry on our shoulders. Gray nerve- 

 tissue is found also in the spinal cord, and some animals, as the frog 

 and the alligator, have more of it in this organ than they have in the 

 brain. It also exists in connection with what is called the sympathetic 

 nerve, in the form of masses called ganglia, and generally placed in 

 intimate relation with the several vital organs of the body — as the 

 heart, stomach, lungs, liver, etc. 



Besides the gray nerve-tissue, there is another kind of nerve-sub- 

 stance called the white, and which, instead of consisting of granular 

 forms or cells, is made up of tubes or fibers. The white nerve-sub- 

 stance has nothing to do with the evolution of nerve-force or mind. 

 Its office is to transmit the nerve-force from the places where it is 

 formed to other parts of the body. The great mass of the brain and 

 of the spinal cord, and the whole of the nerves that ramify through the 

 body, consist of white nerve-tissue. You will understand, therefore, 

 that this substance is analogous to the wires of the telegraph, while 

 the gray substance corresponds to the batteries. 



