LESSON xn 



HISTOLOGY ; OR, THE MINUTE STRUCTURE OF 

 THE TISSUES 



1. The Body built up of Tissues and the Tissues 



of Cells. — In the first chapter attention was directed fx) 

 the obvious fact that the substance of which the body of 

 a man or other of the higher animals is composed, is not 

 of uniform texture throughout ; but that, on the contrary, 

 it is distinguishable into a variety of components which 

 differ very widely from one another, not only in their 

 general appearance, their colour, and their hardness or 

 softness, but also in their chemical composition, and in the 

 properties which they exhibit in the living state. 



lu dissecting a limb there is no difficulty in distinguish- 

 ing tlie bones, the cartilages, the nmscles, the nerves 

 and so forth from one another ; and it is obvious that the 

 other limbs, the trunk, and the head, are chiefly made up 

 of similar structures. Hence, when the foundations of 

 anatomical science were laid, more than two thousand 

 years ago, these "like " structures which occur in different 

 parts of the organism were termed homoiomera, " similar 

 parts." In modern times they have been termed tissxtes, 

 and the branch of biology which is concerned witli the 

 investigation of the nature of these tissues is called 

 Histology. 



Histology is a very large and difficult subject, and this 

 whole book might well be taken up with a thorough dis- 

 cussion of even its elements. But physiohigy is, in 



