30 LETTERS TO BROTHER JOHN. 



of veins. This termination of arteries in veins can 

 be seen, by the aid of the microscope, in the frog 

 and salamander. In some fishes it can be seen with 

 the naked eye. The arteries near their termination, 

 and the veins near their beginning, are many times 

 smaller than the finest hairs ; and, in this state of 

 hairlike minuteness, they constitute that which is 

 called the ultimate tissue of the arteries and veins ; 

 and so, also, the tissue formed by the nerves and 

 absorbent vessels, while in their last state of minute- 

 ness, is called the ultimate tissue of the nerves and 

 absorbents ; and that beautiful network formed by 

 the interlacing of all these delicate and hairlike 

 threads, viz. arteries, veins, nerves, and absorbents, 

 in their minutest condition, is denominated the ulti- 

 mate tissue of the body ; and this ultimate tissue 

 constitutes, in fact, nearly the whole of the body: for 

 all that which appears to our eyes so firm and solid 

 (not even excepting the bones) almost entirely con- 

 sists of this astonishing network of minute vessels 

 and nerves. This network, or ultimate tissue of the 

 body, owes its compactness to its being firmly com- 

 pressed and interwoven ; to its being well and accu- 

 rately filled with fluid (principally blood) ; and to 

 the circumstance of its being everywhere supported, 

 held together, contained, and, as it were, closely 



