CHEMICAL COMPOSITION OF THE BRAIN. 133 



two pairs of nerves proceeding towards the spinal mar- 

 row, one on each side, and inserted into it by two roots. 



Emily. But il these two divisions of the nerves, have 

 their termination, not their origin in the spinal marrow. 

 is it not improper to give them the name of roots % 



j} Tt J5. This name was given them when the nerves 

 were supposed to originate from the spinal . marrow, and 

 is now retained merely for the sake of convenience. 



Emily. Pray, tell me how many nerves go to the 

 spinal marrow in this manner? 



Dr. B. The whole number of spinal nerves is thir- 

 ty-one on each side, and are perfectly regular and sym- 

 metrical. Tracing the spinal marrow upwards into the 

 head, we find it terminated by the oblong marrow, as 

 a column is surmounted by its capital. Nearly all the 

 rest of the brain is distinguished into two portions, the 

 cerebellum, occupying the inferior and posterior parts of 

 the head ; and the cerebrum, which fills up the remain- 

 ing space. Inclosed in its bony case, and enveloped by- 

 thick membranes, this delicate organ has all the securi- 

 ty and protection, which its pre-eminent importance de- 

 mands. The quantity of blood which it receives is re- 

 markably large, for though it does not weigh more than 

 one-fortieth of the whole body, it is estimated that one- 

 tenth of all the blood sent from the heart, goes to this 

 organ. Its external portions are convoluted in structure, 

 and the whole has a soft, pulpy consistence. 



Emily. Has its chemical composition ever been as- 

 certained ? I feel not a little curious to know " what 

 stuff our brains are made of." 



Dr. B. It has been found that about three-fourths of 

 its weight is water, and in the solid parts are considera- 

 ble fat, a peculiar animal principle, called ozmazome, a 

 quantity of albumen, a minute portion of phosphorus, 

 and some salts, chiefly phosphates of lime, soda and am- 

 monia. 



Emily. Fat, phosphorus, lime and soda ! Of all the 

 strange facts which you have related, this seems to be 

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