14. In Fig. 37, you see the general arrangement of the brain. It is a view of one of the halves or hem. ispheres of the brain. It is the inside of the hemisphere that you see. At a b and c is the cerebrum; at f is represented the white substance that joins this hemisphere to the other; at d is the cerebellum,

showing a very beautiful arrangement, called the arbor vitæ, or tree of life; at e is the beginning of the spinal marrow; at g is the beginning of the nerve of sight, and at 7 is the nerve of smell. Then there are various other nerves, which go to the eye and other parts of the face.

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15. You observe that the surface of the brain is very irregular. The brain does not touch the inside of the skull, but it is covered by three different membranes, one of which is very strong and thick, so as to protect this delicate organ from injury.

16. The brain is soft, something like blancmange. It is the softest organ in the body. It is composed of two kinds of substance. These are quite well represented in Fig. 38. Here the upper half of the brain is cut off, and you see the upper cut surface of the

What is said of the surface of the brain, and of its coverings? What 18 the consistence of the brain?

lower half. The outer shaded part is a grayish substance. All on the inside of this is a white substance. You see the dividing line between the two halves or hemispheres. In the middle of the Figure is represented a substance which makes a connection between the hemispheres. It is probably by means of this connection that the two halves of the brain act together as one brain.

17. It is curious to observe that the white part of the brain is just like the nerves. It is, like them, composed of very fine tubes. It is indeed a great central collection of the beginnings of nerves that branch out all over the body.

18. The outer gray part of the brain is, on the other hand, made up of cells, instead of tubes. This is supposed to be the working part of the brain.

The mind acts directly upon the gray part when it moves any of the body. Thus, when you will to have your hand move, the mind does something, but what we know not, to some part of this gray substance. Then an impression or message is sent through those tubes in the white substance which are connected with this part of the gray substance. And as these tubes extend from the brain in the nerves to the muscles of the hand, the hand is moved.

19. In sensation all this is reversed. The impression travels just the contrary way. It goes to the brain, and not from it, as it does in motion. If any one touches you, the impression is carried by the nervous

What are the two kinds of substance in the brain, and how are they arranged? What is the white substance? Of what is the gray substance composed? What is supposed in regard to it? What happens n motion, and what in sensation?

tubes to some portion of the brain. The gray substance at this part of the brain receives the impression from the tubes in the white substance, and so the mind feels it.

20. You observe that I have used the words impression and message in speaking of the communication of the mind, by the nerves, with all parts of the body I use them because they are the best words that I can use in our present state of knowledge on this subject. We do not know what it is that is sent along the nerves. We only know that something passes through these tubes whenever the mind feels anything, or excites the muscles to action. And not knowing what it is, we speak of it as a message or an impression.

21. There have been many suppositions on this subject. Some have supposed that electricity travels along the nerves just as it does along the wires of a telegraph. They suppose that it goes from the brain. when the mind excites the muscles to action, and that it goes towards the brain when we feel any sensation. Others have supposed that there was a vibration or shaking of the substance in the tubes of the nerves from one end of them to the other. But these are mere suppositions, and there is no proof that they are true. Whatever it is that passes through the nerves, it must pass through each of the multitude of little tubes separately, for, as you remember, each tube has no communication with any of the other tubes with which it is bound up.

22. Not only are there different nerves for sensa What has been sup

Do we know what is sent along the nerves? posed in regard to it?