11 



it readily diffuses itself through air and water, and re- 

 sides invisibly in them. And earth eagerly imbibing 

 both air and water, by their means forms the perma- 

 nent basis and growth of all mineral, vegetable, and 

 animal bodies. 



These earthly particles have their connexion and 

 power of cohesion, not from themselves or a mere 

 contact; but from the intermediate glue placed betwixt 

 them. 



That this glue is composed of oil, combined with 

 wafer, by the vital attrition in animals, appears from, 

 the chymical analysis of bones and hair; from the 

 jellyof bones, ivory, and horns ; and from the nature 

 of our ailments themselves. Nor is there any kind 

 of glue that could more powerfully join the parts of 

 animals, as we experience in fish glue, and that v of 

 joiners or cabinet-makers. 



Earthy particles then cohering longitudinally, and 

 tied together by an intervening cohesive glue, com- 

 pose first one of the least or most simple fibres ; such 

 as we have a knowledge of rather from reason than 

 s^nse. 



The finest microscopes have been hitherto insuffi- 

 cient to l<;ad us to a sight of the smallest moving and 

 nervous fibrils, and still less can we ever expect from 

 them, to get any sensible idea of the mechanism by 

 which sensation and motion are effected. 



But the least fibres which appear to the sight are of 

 t\vo kinds. 



Of these .two kinds of fibres, as we shall presently 

 see, we may distinguish the former by the title of fila- 

 mentary, and the latter of membranous. 



The first kind of these fibres is lineal, namely, such 

 a form as makes their length considerably large in 

 proportion to their breadth ; and which, by disposing 

 of the elementary particles in a right line, must of 

 course lay them generally parallel with the neighbour- 

 ing or contiguous iibies. Examples of such fibres we 

 see in me bjat-s, and most easily in those of a foetus ; 

 a iid likewise in tim Un.lons, ligaments, and muscles ; 

 B 6 , 



