134 EVOLUTION, OLD AND NEW. 



manner, difficult though it seems ; but in order that I 

 may do so, I would ask the reader to lend me his atten- 

 tion for a few moments while we regard the brain 

 simply as brain, and have no other idea concerning 

 it than we can derive from inspection and reflection. 

 The brain, as well as the medulla oblongata and the 

 spinal marrow, which are but prolongations of the brain 

 itself, is only a kind of hardly organized mucilage ; we 

 find in it nothing but the extremities of small arteries, 

 which run into it in very great numbers, but which 

 convey a white and nourishing lymph instead of blood. 

 When the parts of the brain are disunited by macera- 

 tion, these same small arteries, or lymphatic vessels, 

 appear as very delicate threads throughout their whole 

 length. The nerves, on the contrary, do not penetrate 

 the substance of the brain ; they abut upon its surface 

 only ; before reaching it they lose their elasticity and 

 solidity, and the extremities of the nerves which are 

 nearest to the brain are soft, and nearly mucilaginous. 

 From this exposition, in which there is nothing hypo- 

 thetical, it appears that the brain, which is nourished by 

 the lymphatic arteries, does in its turn provide nourish- 

 ment for the nerves, and that we must regard these as 

 a kind of vegetation which rises as trunks and branches 

 from the brain, and become subsequently subdivided 

 into an infinite number, as it were, of twigs. The brain 

 is to the nerves what the earth is to plants: the last 

 extremities of the nerves are the roots, which with every 

 vegetable are more soft and tender than the trunk or 

 branches; they contain a ductile matter fit for the 

 growth and nourishment of the nervous tree or fibre; 



