66 LETTERS TO BROTHER JOHN. 



one, to represent the arteries; a black one, to repre- 

 sent the veins ; a white one, for the nerves ; and a 

 silver one, for the absorbents. Dip them in melted 

 wax, and then roll them up into a firm ball. This 

 will give you a rude idea of the manner in which 

 minute threadlike vessels can be so arranged as to 

 form a solid mass ; for it is easy to fancy three of 

 these threads to be hollow tubes filled with fluid, 

 like arteries, veins, and absorbents. The wax, 

 which everywhere surrounds them and glues them 

 together, will afford you some notion of the prin- 

 cipal office of the cellular web; which is, to hold 

 the different parts of the intimate structure of the 

 body together, by entangling them in its meshes, 

 as the wax unites the threads by virtue of its sticki- 

 ness. If, instead of dipping the threads into melted 

 wax, you had dipped them in a solution of phos- 

 phate of lime (which constitutes the hard part of 

 bones), the ball, when dry, would have given no 

 bad representation of the structure of the bones. 



Now, suppose the former ball that formed of 

 the threads dipped in wax to be submitted to a 

 pressure capable of flattening it until it becomes no 

 thicker than a film of tissue-paper. This will shew 

 you how the same structure which forms the thick, 

 solid, and gross parts of the body may be so 



